diff --git a/ojosama_test.go b/ojosama_test.go
index a83600c..a8a800a 100644
--- a/ojosama_test.go
+++ b/ojosama_test.go
@@ -529,6 +529,13 @@ func TestConvert(t *testing.T) {
 			opt:     nil,
 			wantErr: false,
 		},
+		{
+			desc:    "正常系: なん(じゃ|や|だ)は、いずれも「なんですの」に変換いたしますわ",
+			src:     "なんじゃこれ。なんだこれ。なんやこれ。",
+			want:    "なんですのこちら。なんですのこちら。なんですのこちら。",
+			opt:     nil,
+			wantErr: false,
+		},
 	}
 
 	for _, tt := range tests {
diff --git a/rule.go b/rule.go
index f1a5acb..eb14f38 100644
--- a/rule.go
+++ b/rule.go
@@ -175,6 +175,28 @@ var (
 				newCond([]string{"助詞", "終助詞"}, "よ"),
 			},
 		},
+
+		{
+			Value: "なんですの",
+			Conditions: []convertConditions{
+				newCond(pronounGeneral, "なん"),
+				newCond(verbsSubAssistant, "じゃ"),
+			},
+		},
+		{
+			Value: "なんですの",
+			Conditions: []convertConditions{
+				newCond(pronounGeneral, "なん"),
+				newCond(auxiliaryVerb, "だ"),
+			},
+		},
+		{
+			Value: "なんですの",
+			Conditions: []convertConditions{
+				newCond(pronounGeneral, "なん"),
+				newCond(assistantParallel, "や"),
+			},
+		},
 	}
 
 	// excludeRules は変換処理を無視するルール。
@@ -695,6 +717,8 @@ var (
 	verbs                    = []string{"感動詞"}
 	verbIndependence         = []string{"動詞", "自立"}
 	sentenceEndingParticle   = []string{"助詞", "終助詞"}
+	verbsSubAssistant        = []string{"助詞", "副助詞"}
+	assistantParallel        = []string{"助詞", "並立助詞"}
 	auxiliaryVerb            = []string{"助動詞"}
 	nounsSaDynamic           = []string{"名詞", "サ変接続"}
 )