diff --git a/CHANGELOG.md b/CHANGELOG.md
index 310d8951c1..cec57d3f81 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Enhancements
 ### Bug Fixes
 * Fix use-after-free case on nmslib search path [#1305](https://github.com/opensearch-project/k-NN/pull/1305)
+* Fixed field value from nested mapping when train model [#1318](https://github.com/opensearch-project/k-NN/pull/1318)
 ### Infrastructure
 * Upgrade gradle to 8.4 [1289](https://github.com/opensearch-project/k-NN/pull/1289)
 ### Documentation
diff --git a/src/main/java/org/opensearch/knn/index/IndexUtil.java b/src/main/java/org/opensearch/knn/index/IndexUtil.java
index 574e4a9773..a38291fcbc 100644
--- a/src/main/java/org/opensearch/knn/index/IndexUtil.java
+++ b/src/main/java/org/opensearch/knn/index/IndexUtil.java
@@ -28,6 +28,7 @@
 import java.util.HashMap;
 import java.util.Map;
 
+import static org.opensearch.index.mapper.MapperService.INDEX_MAPPING_NESTED_FIELDS_LIMIT_SETTING;
 import static org.opensearch.knn.common.KNNConstants.BYTES_PER_KILOBYTES;
 import static org.opensearch.knn.common.KNNConstants.HNSW_ALGO_EF_SEARCH;
 import static org.opensearch.knn.common.KNNConstants.SPACE_TYPE;
@@ -59,6 +60,39 @@ public static int getFileSizeInKB(String filePath) {
         return Math.toIntExact((file.length() / BYTES_PER_KILOBYTES) + 1L); // Add one so that integer division rounds up
     }
 
+    /**
+     * This method retrieves a specified field mapping from a set of mapping properties.
+     *
+     * @param properties A map representing properties, where each key is a property name and
+     *                   the value is either a sub-map of properties or the property value itself.
+     * @param fieldPaths The field path list that make up the path to the field mapping.
+     * @return           The value of the field if found, or null if the field is not present in the map.
+     */
+    public static Object getFieldMapping(final Map<String, Object> properties, final String[] fieldPaths) {
+        Object currentFieldMapping = properties;
+
+        for (String path : fieldPaths) {
+            if (!(currentFieldMapping instanceof Map<?, ?>)) {
+                return null;
+            }
+
+            currentFieldMapping = ((Map<String, Object>) currentFieldMapping).get(path);
+            if (currentFieldMapping == null) {
+                return null;
+            }
+
+            if (currentFieldMapping instanceof Map<?, ?>) {
+                Object possibleProperties = ((Map<String, Object>) currentFieldMapping).get("properties");
+                if (possibleProperties instanceof Map<?, ?>) {
+                    currentFieldMapping = possibleProperties;
+                }
+            }
+        }
+
+        return currentFieldMapping;
+    }
+
+
     /**
      * Validate that a field is a k-NN vector field and has the expected dimension
      *
@@ -100,7 +134,24 @@ public static ValidationException validateKnnField(
             return exception;
         }
 
-        Object fieldMapping = properties.get(field);
+        // Check field path is valid
+        if (field.isEmpty()) {
+            exception.addValidationError("Field path is empty");
+            return exception;
+        }
+
+        String[] fieldPaths = field.split("\\.");
+
+        Long nestedFieldMaxLimit = INDEX_MAPPING_NESTED_FIELDS_LIMIT_SETTING.get(indexMetadata.getSettings());
+
+        // Check filed path length is valid
+        if (fieldPaths.length == 0 || fieldPaths.length > nestedFieldMaxLimit) {
+            exception.addValidationError(String.format("Field path length \"%s\" is invalid, it should > 0 and <= %d",
+                field, nestedFieldMaxLimit));
+            return exception;
+        }
+
+        Object fieldMapping = getFieldMapping(properties, fieldPaths);
 
         // Check field existence
         if (fieldMapping == null) {
diff --git a/src/main/java/org/opensearch/knn/training/VectorReader.java b/src/main/java/org/opensearch/knn/training/VectorReader.java
index c104e2df36..ef935d870e 100644
--- a/src/main/java/org/opensearch/knn/training/VectorReader.java
+++ b/src/main/java/org/opensearch/knn/training/VectorReader.java
@@ -29,6 +29,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Map;
 import java.util.function.Consumer;
 
 public class VectorReader {
@@ -182,9 +183,21 @@ public void onResponse(SearchResponse searchResponse) {
             int vectorsToAdd = Integer.min(maxVectorCount - collectedVectorCount, hits.length);
             List<Float[]> trainingData = new ArrayList<>();
 
-            for (int i = 0; i < vectorsToAdd; i++) {
+            for (int vector = 0; vector < vectorsToAdd; vector++) {
+                Map<String, Object> sourceMap = hits[vector].getSourceAsMap();
+                // The field name may be a nested field, so we need to split it and traverse the map.
+                // Example fieldName: "my_field" or "my_field.nested_field.nested_nested_field"
+                String[] fieldPath = fieldName.split("\\.");
+                Map<String, Object> currentMap = sourceMap;
+
+                for (int pathPart = 0; pathPart < fieldPath.length - 1; pathPart++) {
+                    currentMap = (Map<String, Object>) currentMap.get(fieldPath[pathPart]);
+                }
+
+                List<Number> fieldList = (List<Number>) currentMap.get(fieldPath[fieldPath.length - 1]);
+
                 trainingData.add(
-                    ((List<Number>) hits[i].getSourceAsMap().get(fieldName)).stream().map(Number::floatValue).toArray(Float[]::new)
+                        fieldList.stream().map(Number::floatValue).toArray(Float[]::new)
                 );
             }
 
diff --git a/src/test/java/org/opensearch/knn/KNNSingleNodeTestCase.java b/src/test/java/org/opensearch/knn/KNNSingleNodeTestCase.java
index 38037a7fe3..bf4341d3a8 100644
--- a/src/test/java/org/opensearch/knn/KNNSingleNodeTestCase.java
+++ b/src/test/java/org/opensearch/knn/KNNSingleNodeTestCase.java
@@ -89,6 +89,36 @@ protected void createKnnIndexMapping(String indexName, String fieldName, Integer
         request.source(fieldName, "type=knn_vector,dimension=" + dimensions);
         OpenSearchAssertions.assertAcked(client().admin().indices().putMapping(request).actionGet());
     }
+    /**
+     * Create simple k-NN mapping which can be nested.
+     * e.g. fieldPath = "a.b.c" will create mapping for "c" as knn_vector
+     */
+    protected void createKnnNestedIndexMapping(String indexName, String fieldPath, Integer dimensions)
+            throws IOException {
+        PutMappingRequest request = new PutMappingRequest(indexName);
+        String[] path = fieldPath.split("\\.");
+        XContentBuilder xContentBuilder = XContentFactory.jsonBuilder().startObject().startObject("properties");
+        for (int i = 0; i < path.length; i++) {
+            xContentBuilder.startObject(path[i]);
+            if (i == path.length - 1) {
+                xContentBuilder.field("type", "knn_vector")
+                        .field("dimension", dimensions.toString());
+            } else {
+                xContentBuilder.startObject("properties");
+            }
+        }
+        for (int i = path.length - 1; i >= 0; i--) {
+            if (i != path.length - 1) {
+                xContentBuilder.endObject();
+            }
+            xContentBuilder.endObject();
+        }
+        xContentBuilder.endObject().endObject();
+
+        request.source(xContentBuilder);
+
+        OpenSearchAssertions.assertAcked(client().admin().indices().putMapping(request).actionGet());
+    }
 
     /**
      * Get default k-NN settings for test cases
@@ -112,6 +142,31 @@ protected void addKnnDoc(String index, String docId, String fieldName, Object[]
         assertEquals(response.status(), RestStatus.CREATED);
     }
 
+    /**
+     * Add a k-NN doc to an index with nested knn_vector field
+     */
+    protected void addKnnNestedDoc(String index, String docId, String fieldPath, Object[] vector) throws IOException, InterruptedException,
+        ExecutionException {
+        XContentBuilder builder = XContentFactory.jsonBuilder().startObject();
+        String[] fieldParts = fieldPath.split("\\.");
+
+        for (int i = 0; i < fieldParts.length - 1; i++) {
+            builder.startObject(fieldParts[i]);
+        }
+        builder.field(fieldParts[fieldParts.length - 1], vector);
+        for (int i = fieldParts.length - 2; i >= 0; i--) {
+            builder.endObject();
+        }
+        builder.endObject();
+        IndexRequest indexRequest = new IndexRequest().index(index)
+            .id(docId)
+            .source(builder)
+            .setRefreshPolicy(WriteRequest.RefreshPolicy.IMMEDIATE);
+
+        IndexResponse response = client().index(indexRequest).get();
+        assertEquals(response.status(), RestStatus.CREATED);
+    }
+
     /**
      * Add any document to index
      */
diff --git a/src/test/java/org/opensearch/knn/index/IndexUtilTests.java b/src/test/java/org/opensearch/knn/index/IndexUtilTests.java
index 7013ef261a..4efe281130 100644
--- a/src/test/java/org/opensearch/knn/index/IndexUtilTests.java
+++ b/src/test/java/org/opensearch/knn/index/IndexUtilTests.java
@@ -20,6 +20,8 @@
 import org.opensearch.knn.KNNTestCase;
 import org.opensearch.knn.index.util.KNNEngine;
 
+import java.util.Collections;
+import java.util.HashMap;
 import java.util.Map;
 
 import static org.mockito.ArgumentMatchers.anyString;
@@ -67,4 +69,34 @@ public void testGetLoadParameters() {
         assertEquals(spaceType2.getValue(), loadParameters.get(SPACE_TYPE));
         assertEquals(efSearchValue, loadParameters.get(HNSW_ALGO_EF_SEARCH));
     }
+
+    public void testGetFieldMappingNonNestedField() {
+        Map<String, Object> fieldValues = Map.of("type", "knn_vector", "dimension", 8);
+        Map<String, Object> properties = Map.of("top_level_field", fieldValues);
+        String[] field = {"top_level_field"};
+
+        Object result = IndexUtil.getFieldMapping(properties, field);
+        assertEquals(fieldValues, result);
+    }
+
+    public void testGetFieldMappingNestedField() {
+        Map<String, Object> deepFieldValues = Map.of("type", "knn_vector", "dimension", 8);
+        Map<String, Object> deepField = Map.of("train-field", deepFieldValues);
+        Map<String, Object> deepFieldProperties = Map.of("properties", deepField);
+        Map<String, Object> nest_b = Map.of("b", deepFieldProperties);
+        Map<String, Object> nest_b_properties = Map.of("properties", nest_b);
+        Map<String, Object> nest_a = Map.of("a", nest_b_properties);
+        String[] field = {"a", "b", "train-field"};
+
+        Object deepResult = IndexUtil.getFieldMapping(nest_a, field);
+        assertEquals(deepFieldValues, deepResult);
+    }
+
+    public void testGetFieldMappingEmptyProperties() {
+        Map<String, Object> properties = Collections.emptyMap();
+        String[] field = {"top_level_field"};
+
+        Object result = IndexUtil.getFieldMapping(properties, field);
+        assertNull(result);
+    }
 }
diff --git a/src/test/java/org/opensearch/knn/plugin/action/RestTrainModelHandlerIT.java b/src/test/java/org/opensearch/knn/plugin/action/RestTrainModelHandlerIT.java
index 545fa7cc7f..1180dcf0a3 100644
--- a/src/test/java/org/opensearch/knn/plugin/action/RestTrainModelHandlerIT.java
+++ b/src/test/java/org/opensearch/knn/plugin/action/RestTrainModelHandlerIT.java
@@ -341,4 +341,74 @@ public void testTrainModel_success_noId() throws Exception {
 
         assertTrainingSucceeds(modelId, 30, 1000);
     }
+
+    // Test to checks when user tries to train a model with nested fields
+    public void testTrainModel_success_nestedField() throws Exception {
+        String modelId = "test-model-id";
+        String trainingIndexName = "train-index";
+        String nestedFieldPath = "a.b.train-field";
+        int dimension = 8;
+
+        // Create a training index and randomly ingest data into it
+        String mapping = createKnnIndexNestedMapping(dimension, nestedFieldPath);
+        createKnnIndex(trainingIndexName, mapping);
+        int trainingDataCount = 200;
+        bulkIngestRandomVectorsWithNestedField(trainingIndexName, nestedFieldPath, trainingDataCount, dimension);
+
+        // Call the train API with this definition:
+        /*
+            {
+                "training_index": "train_index",
+                "training_field": "a.b.train_field",
+                "dimension": 8,
+                "description": "this should be allowed to be null",
+                "method": {
+                    "name":"ivf",
+                    "engine":"faiss",
+                    "space_type": "l2",
+                    "parameters":{
+                        "nlist":1,
+                        "encoder":{
+                            "name":"pq",
+                            "parameters":{
+                                "code_size":2,
+                                "m": 2
+                            }
+                        }
+                    }
+                }
+             }
+         */
+        XContentBuilder builder = XContentFactory.jsonBuilder()
+            .startObject()
+            .field(NAME, "ivf")
+            .field(KNN_ENGINE, "faiss")
+            .field(METHOD_PARAMETER_SPACE_TYPE, "l2")
+            .startObject(PARAMETERS)
+            .field(METHOD_PARAMETER_NLIST, 1)
+            .startObject(METHOD_ENCODER_PARAMETER)
+            .field(NAME, "pq")
+            .startObject(PARAMETERS)
+            .field(ENCODER_PARAMETER_PQ_CODE_SIZE, 2)
+            .field(ENCODER_PARAMETER_PQ_M, 2)
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject();
+        Map<String, Object> method = xContentBuilderToMap(builder);
+
+        Response trainResponse = trainModel(modelId, trainingIndexName, nestedFieldPath, dimension, method, "dummy description");
+
+        assertEquals(RestStatus.OK, RestStatus.fromCode(trainResponse.getStatusLine().getStatusCode()));
+
+        Response getResponse = getModel(modelId, null);
+        String responseBody = EntityUtils.toString(getResponse.getEntity());
+        assertNotNull(responseBody);
+
+        Map<String, Object> responseMap = createParser(MediaTypeRegistry.getDefaultMediaType().xContent(), responseBody).map();
+
+        assertEquals(modelId, responseMap.get(MODEL_ID));
+
+        assertTrainingSucceeds(modelId, 30, 1000);
+    }
 }
diff --git a/src/test/java/org/opensearch/knn/training/VectorReaderTests.java b/src/test/java/org/opensearch/knn/training/VectorReaderTests.java
index 74008a0435..b7372e6086 100644
--- a/src/test/java/org/opensearch/knn/training/VectorReaderTests.java
+++ b/src/test/java/org/opensearch/knn/training/VectorReaderTests.java
@@ -34,6 +34,7 @@ public class VectorReaderTests extends KNNSingleNodeTestCase {
     private final static int DEFAULT_LATCH_TIMEOUT = 100;
     private final static String DEFAULT_INDEX_NAME = "test-index";
     private final static String DEFAULT_FIELD_NAME = "test-field";
+    private final static String DEFAULT_NESTED_FIELD_PATH = "a.b.test-field";
     private final static int DEFAULT_DIMENSION = 16;
     private final static int DEFAULT_NUM_VECTORS = 100;
     private final static int DEFAULT_MAX_VECTOR_COUNT = 10000;
@@ -345,6 +346,46 @@ public void testRead_invalid_fieldIsNotKnn() throws InterruptedException, Execut
         );
     }
 
+    public void testRead_valid_NestedField() throws InterruptedException, ExecutionException, IOException {
+        createIndex(DEFAULT_INDEX_NAME);
+        createKnnNestedIndexMapping(DEFAULT_INDEX_NAME, DEFAULT_NESTED_FIELD_PATH, DEFAULT_DIMENSION);
+
+        // Create list of random vectors and ingest
+        Random random = new Random();
+        List<Float[]> vectors = new ArrayList<>();
+        for (int i = 0; i < DEFAULT_NUM_VECTORS; i++) {
+            Float[] vector = random.doubles(DEFAULT_DIMENSION).boxed().map(Double::floatValue).toArray(Float[]::new);
+            vectors.add(vector);
+            addKnnNestedDoc(DEFAULT_INDEX_NAME, Integer.toString(i), DEFAULT_NESTED_FIELD_PATH, vector);
+        }
+
+        // Configure VectorReader
+        ClusterService clusterService = node().injector().getInstance(ClusterService.class);
+        VectorReader vectorReader = new VectorReader(client());
+
+        // Read all vectors and confirm they match vectors
+        TestVectorConsumer testVectorConsumer = new TestVectorConsumer();
+        final CountDownLatch inProgressLatch = new CountDownLatch(1);
+        vectorReader.read(
+                clusterService,
+                DEFAULT_INDEX_NAME,
+                DEFAULT_NESTED_FIELD_PATH,
+                DEFAULT_MAX_VECTOR_COUNT,
+                DEFAULT_SEARCH_SIZE,
+                testVectorConsumer,
+                createOnSearchResponseCountDownListener(inProgressLatch)
+        );
+
+        assertLatchDecremented(inProgressLatch);
+
+        List<Float[]> consumedVectors = testVectorConsumer.getVectorsConsumed();
+        assertEquals(DEFAULT_NUM_VECTORS, consumedVectors.size());
+
+        List<Float> flatVectors = vectors.stream().flatMap(Arrays::stream).collect(Collectors.toList());
+        List<Float> flatConsumedVectors = consumedVectors.stream().flatMap(Arrays::stream).collect(Collectors.toList());
+        assertEquals(new HashSet<>(flatVectors), new HashSet<>(flatConsumedVectors));
+    }
+
     private static class TestVectorConsumer implements Consumer<List<Float[]>> {
 
         List<Float[]> vectorsConsumed;
diff --git a/src/testFixtures/java/org/opensearch/knn/KNNRestTestCase.java b/src/testFixtures/java/org/opensearch/knn/KNNRestTestCase.java
index 642b8bfb92..15f3a4c160 100644
--- a/src/testFixtures/java/org/opensearch/knn/KNNRestTestCase.java
+++ b/src/testFixtures/java/org/opensearch/knn/KNNRestTestCase.java
@@ -356,6 +356,41 @@ protected String createKnnIndexMapping(List<String> fieldNames, List<Integer> di
         return xContentBuilder.toString();
     }
 
+    /**
+     * Utility to create a Knn Index Mapping with nested field
+     *
+     * @param dimensions dimension of the vector
+     * @param fieldPath  path of the nested field, e.g. "my_nested_field.my_vector"
+     * @return mapping string for the nested field
+     */
+    protected String createKnnIndexNestedMapping(Integer dimensions, String fieldPath) throws IOException {
+        String[] fieldPathArray = fieldPath.split("\\.");
+        XContentBuilder xContentBuilder = XContentFactory.jsonBuilder().startObject().startObject("properties");
+
+        for (int i = 0; i < fieldPathArray.length; i++) {
+            xContentBuilder.startObject(fieldPathArray[i]);
+            if (i == fieldPathArray.length - 1) {
+                xContentBuilder.field("type", "knn_vector")
+                        .field("dimension", dimensions.toString());
+            } else {
+                xContentBuilder.startObject("properties");
+            }
+        }
+
+        for (int i = fieldPathArray.length - 1; i >= 0; i--) {
+            if (i != fieldPathArray.length - 1) {
+                xContentBuilder.endObject();
+            }
+            xContentBuilder.endObject();
+        }
+
+        xContentBuilder.endObject().endObject();
+
+        return xContentBuilder.toString();
+    }
+
+
+
     /**
      * Get index mapping as map
      *
@@ -423,6 +458,37 @@ protected void addKnnDoc(String index, String docId, String fieldName, Object[]
         assertEquals(request.getEndpoint() + ": failed", RestStatus.OK, RestStatus.fromCode(response.getStatusLine().getStatusCode()));
     }
 
+    /**
+     * Add a single KNN Doc to an index with a nested vector field
+     *
+     * @param index           name of the index
+     * @param docId           id of the document
+     * @param nestedFieldPath path of the nested field, e.g. "my_nested_field.my_vector"
+     * @param vector          vector to add
+     *
+     */
+    protected void addKnnDocWithNestedField(String index, String docId, String nestedFieldPath, Object[] vector) throws IOException {
+        String[] fieldParts = nestedFieldPath.split("\\.");
+
+        XContentBuilder builder = XContentFactory.jsonBuilder().startObject();
+        for (int i = 0; i < fieldParts.length - 1; i++) {
+            builder.startObject(fieldParts[i]);
+        }
+        builder.field(fieldParts[fieldParts.length - 1], vector);
+        for (int i = fieldParts.length - 2; i >= 0; i--) {
+            builder.endObject();
+        }
+        builder.endObject();
+
+        Request request = new Request("POST", "/" + index + "/_doc/" + docId + "?refresh=true");
+        request.setJsonEntity(builder.toString());
+        client().performRequest(request);
+
+        request = new Request("POST", "/" + index + "/_refresh");
+        Response response = client().performRequest(request);
+        assertEquals(request.getEndpoint() + ": failed", RestStatus.OK, RestStatus.fromCode(response.getStatusLine().getStatusCode()));
+    }
+
     /**
      * Add a single KNN Doc to an index with multiple fields
      */
@@ -853,6 +919,25 @@ public void bulkIngestRandomVectors(String indexName, String fieldName, int numV
 
     }
 
+    /**
+     * Bulk ingest random vectors with nested field
+     *
+     * @param indexName       index name
+     * @param nestedFieldPath nested field path, e.g. "my_nested_field.my_vector_field"
+     * @param numVectors      number of vectors
+     * @param dimension       vector dimension
+     */
+    public void bulkIngestRandomVectorsWithNestedField(String indexName, String nestedFieldPath, int numVectors, int dimension) throws IOException {
+        for (int i = 0; i < numVectors; i++) {
+            float[] vector = new float[dimension];
+            for (int j = 0; j < dimension; j++) {
+                vector[j] = randomFloat();
+            }
+
+            addKnnDocWithNestedField(indexName, String.valueOf(i + 1), nestedFieldPath, Floats.asList(vector).toArray());
+        }
+    }
+
     // Method that adds multiple documents into the index using Bulk API
     public void bulkAddKnnDocs(String index, String fieldName, float[][] indexVectors, int docCount) throws IOException {
         Request request = new Request("POST", "/_bulk");