diff --git a/tests/system/test_gbq.py b/tests/system/test_gbq.py
index feb4d9f3..5b90e8ba 100644
--- a/tests/system/test_gbq.py
+++ b/tests/system/test_gbq.py
@@ -1014,7 +1014,7 @@ def test_upload_data_with_timestamp(self, project_id):
                 "2018-07-13T05:40:45.348318",
                 "2018-08-13T05:40:45.348318",
             ],
-            dtype="datetime64[us]",
+            dtype="datetime64[ns]",
         ).dt.tz_localize("UTC")
 
         gbq.to_gbq(
@@ -1027,7 +1027,6 @@ def test_upload_data_with_timestamp(self, project_id):
         result_df = gbq.read_gbq(
             "SELECT * FROM {0}".format(self.destination_table + test_id),
             project_id=project_id,
-            dtypes={"times": "datetime64[us]"},
             credentials=self.credentials,
             dialect="legacy",
         )
diff --git a/tests/system/test_read_gbq.py b/tests/system/test_read_gbq.py
index d709bb89..f9358ef6 100644
--- a/tests/system/test_read_gbq.py
+++ b/tests/system/test_read_gbq.py
@@ -149,7 +149,7 @@ def writable_table(
                                 "2011-10-01 00:01:02.345678",
                                 "2018-04-11 23:59:59.999999",
                             ],
-                            dtype="datetime64[us]",
+                            dtype="datetime64[ns]",
                         ),
                         "float_col": [1.125, -2.375, 0.0],
                         "int64_col": pandas.Series(
@@ -175,7 +175,7 @@ def writable_table(
                                 "2011-10-01 00:01:02.345678",
                                 "2018-04-11 23:59:59.999999",
                             ],
-                            dtype="datetime64[us]",
+                            dtype="datetime64[ns]",
                         ).dt.tz_localize(datetime.timezone.utc),
                     }
                 ),
@@ -283,7 +283,7 @@ def writable_table(
                                 "2011-10-01 00:01:02.345678",
                                 None,
                             ],
-                            dtype="datetime64[us]",
+                            dtype="datetime64[ns]",
                         ),
                         "float_col": [None, -2.375, 0.0],
                         "int64_col": pandas.Series([-1, None, 0], dtype="Int64"),
@@ -303,7 +303,7 @@ def writable_table(
                                 None,
                                 "2018-04-11 23:59:59.999999",
                             ],
-                            dtype="datetime64[us]",
+                            dtype="datetime64[ns]",
                         ).dt.tz_localize(datetime.timezone.utc),
                     }
                 ),
@@ -383,7 +383,7 @@ def writable_table(
                         ),
                         "datetime_col": pandas.Series(
                             [None],
-                            dtype="datetime64[us]",
+                            dtype="datetime64[ns]",
                         ),
                         "float_col": pandas.Series([None], dtype="float64"),
                         "int64_col": pandas.Series([None], dtype="Int64"),
@@ -395,7 +395,7 @@ def writable_table(
                         ),
                         "timestamp_col": pandas.Series(
                             [None],
-                            dtype="datetime64[us]",
+                            dtype="datetime64[ns]",
                         ).dt.tz_localize(datetime.timezone.utc),
                     }
                 ),
@@ -552,9 +552,6 @@ def test_default_dtypes(
     result = read_gbq(
         query,
         use_bqstorage_api=use_bqstorage_api,
-        dtypes={"datetime_col": "datetime64[us]",
-                "timestamp_col": "datetime64[us, UTC]",
-        },
         configuration={"query": {"useQueryCache": False}},
     )
     pandas.testing.assert_frame_equal(result, expected)