diff --git a/libs/langchain/langchain/chat_models/azureml_endpoint.py b/libs/langchain/langchain/chat_models/azureml_endpoint.py
index 53bdc84925..8efa957ad0 100644
--- a/libs/langchain/langchain/chat_models/azureml_endpoint.py
+++ b/libs/langchain/langchain/chat_models/azureml_endpoint.py
@@ -4,7 +4,7 @@ from typing import Any, Dict, List, Optional, cast
 from langchain.callbacks.manager import CallbackManagerForLLMRun
 from langchain.chat_models.base import SimpleChatModel
 from langchain.llms.azureml_endpoint import AzureMLEndpointClient, ContentFormatterBase
-from langchain.pydantic_v1 import validator
+from langchain.pydantic_v1 import SecretStr, validator
 from langchain.schema.messages import (
     AIMessage,
     BaseMessage,
@@ -12,7 +12,7 @@ from langchain.schema.messages import (
     HumanMessage,
     SystemMessage,
 )
-from langchain.utils import get_from_dict_or_env
+from langchain.utils import convert_to_secret_str, get_from_dict_or_env
 
 
 class LlamaContentFormatter(ContentFormatterBase):
@@ -94,7 +94,7 @@ class AzureMLChatOnlineEndpoint(SimpleChatModel):
     """URL of pre-existing Endpoint. Should be passed to constructor or specified as 
         env var `AZUREML_ENDPOINT_URL`."""
 
-    endpoint_api_key: str = ""
+    endpoint_api_key: SecretStr = convert_to_secret_str("")
     """Authentication Key for Endpoint. Should be passed to constructor or specified as
         env var `AZUREML_ENDPOINT_API_KEY`."""
 
@@ -112,13 +112,15 @@ class AzureMLChatOnlineEndpoint(SimpleChatModel):
     @classmethod
     def validate_client(cls, field_value: Any, values: Dict) -> AzureMLEndpointClient:
         """Validate that api key and python package exist in environment."""
-        endpoint_key = get_from_dict_or_env(
-            values, "endpoint_api_key", "AZUREML_ENDPOINT_API_KEY"
+        values["endpoint_api_key"] = convert_to_secret_str(
+            get_from_dict_or_env(values, "endpoint_api_key", "AZUREML_ENDPOINT_API_KEY")
         )
         endpoint_url = get_from_dict_or_env(
             values, "endpoint_url", "AZUREML_ENDPOINT_URL"
         )
-        http_client = AzureMLEndpointClient(endpoint_url, endpoint_key)
+        http_client = AzureMLEndpointClient(
+            endpoint_url, values["endpoint_api_key"].get_secret_value()
+        )
         return http_client
 
     @property
diff --git a/libs/langchain/tests/unit_tests/chat_models/test_azureml_endpoint.py b/libs/langchain/tests/unit_tests/chat_models/test_azureml_endpoint.py
new file mode 100644
index 0000000000..de1055fc3d
--- /dev/null
+++ b/libs/langchain/tests/unit_tests/chat_models/test_azureml_endpoint.py
@@ -0,0 +1,65 @@
+"""Test AzureML chat endpoint."""
+
+import os
+
+import pytest
+from pytest import CaptureFixture, FixtureRequest
+
+from langchain.chat_models.azureml_endpoint import AzureMLChatOnlineEndpoint
+from langchain.pydantic_v1 import SecretStr
+
+
+@pytest.fixture(scope="class")
+def api_passed_via_environment_fixture() -> AzureMLChatOnlineEndpoint:
+    """Fixture to create an AzureMLChatOnlineEndpoint instance
+    with API key passed from environment"""
+    os.environ["AZUREML_ENDPOINT_API_KEY"] = "my-api-key"
+    azure_chat = AzureMLChatOnlineEndpoint(
+        endpoint_url="https://<your-endpoint>.<your_region>.inference.ml.azure.com/score"
+    )
+    del os.environ["AZUREML_ENDPOINT_API_KEY"]
+    return azure_chat
+
+
+@pytest.fixture(scope="class")
+def api_passed_via_constructor_fixture() -> AzureMLChatOnlineEndpoint:
+    """Fixture to create an AzureMLChatOnlineEndpoint instance
+    with API key passed from constructor"""
+    azure_chat = AzureMLChatOnlineEndpoint(
+        endpoint_url="https://<your-endpoint>.<your_region>.inference.ml.azure.com/score",
+        endpoint_api_key="my-api-key",
+    )
+    return azure_chat
+
+
+@pytest.mark.parametrize(
+    "fixture_name",
+    ["api_passed_via_constructor_fixture", "api_passed_via_environment_fixture"],
+)
+class TestAzureMLChatOnlineEndpoint:
+    def test_api_key_is_secret_string(
+        self, fixture_name: str, request: FixtureRequest
+    ) -> None:
+        """Test that the API key is a SecretStr instance"""
+        azure_chat = request.getfixturevalue(fixture_name)
+        assert isinstance(azure_chat.endpoint_api_key, SecretStr)
+
+    def test_api_key_masked(
+        self, fixture_name: str, request: FixtureRequest, capsys: CaptureFixture
+    ) -> None:
+        """Test that the API key is masked"""
+        azure_chat = request.getfixturevalue(fixture_name)
+        print(azure_chat.endpoint_api_key, end="")
+        captured = capsys.readouterr()
+        assert (
+            (str(azure_chat.endpoint_api_key) == "**********")
+            and (repr(azure_chat.endpoint_api_key) == "SecretStr('**********')")
+            and (captured.out == "**********")
+        )
+
+    def test_api_key_is_readable(
+        self, fixture_name: str, request: FixtureRequest
+    ) -> None:
+        """Test that the real secret value of the API key can be read"""
+        azure_chat = request.getfixturevalue(fixture_name)
+        assert azure_chat.endpoint_api_key.get_secret_value() == "my-api-key"