diff --git a/sdk/textanalytics/azure-ai-textanalytics/azure/ai/textanalytics/_models.py b/sdk/textanalytics/azure-ai-textanalytics/azure/ai/textanalytics/_models.py
index c95585f76ed6..4db9f79f5639 100644
--- a/sdk/textanalytics/azure-ai-textanalytics/azure/ai/textanalytics/_models.py
+++ b/sdk/textanalytics/azure-ai-textanalytics/azure/ai/textanalytics/_models.py
@@ -43,6 +43,9 @@ def __ne__(self, other):
         """Compare objects by comparing all attributes."""
         return not self.__eq__(other)
 
+    def __contains__(self, key):
+        return key in self.__dict__
+
     def __str__(self):
         return str({k: v for k, v in self.__dict__.items() if not k.startswith('_')})
 
diff --git a/sdk/textanalytics/azure-ai-textanalytics/tests/test_dict_mixin.py b/sdk/textanalytics/azure-ai-textanalytics/tests/test_dict_mixin.py
new file mode 100644
index 000000000000..d308488a9e03
--- /dev/null
+++ b/sdk/textanalytics/azure-ai-textanalytics/tests/test_dict_mixin.py
@@ -0,0 +1,18 @@
+# coding=utf-8
+# ------------------------------------
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+# ------------------------------------
+
+import pytest
+from azure.ai.textanalytics import _models
+
+
+class TestDictMixin:
+
+    def test_contains(self):
+        model = _models.DictMixin()
+        key = "name"
+        value = "steve"
+        model.__setitem__(key, value)
+        assert model.__contains__(key)