diff --git a/libs/partners/openai/langchain_openai/chat_models/base.py b/libs/partners/openai/langchain_openai/chat_models/base.py
index baaa74f637b31..233fa8700a436 100644
--- a/libs/partners/openai/langchain_openai/chat_models/base.py
+++ b/libs/partners/openai/langchain_openai/chat_models/base.py
@@ -480,6 +480,15 @@ def build_extra(cls, values: Dict[str, Any]) -> Any:
         values = _build_model_kwargs(values, all_required_field_names)
         return values
 
+    @model_validator(mode="before")
+    @classmethod
+    def validate_temperature(cls, values: Dict[str, Any]) -> Any:
+        """Currently o1 models only allow temperature=1."""
+        model = values.get("model_name") or values.get("model") or ""
+        if model.startswith("o1") and "temperature" not in values:
+            values["temperature"] = 1
+        return values
+
     @model_validator(mode="after")
     def validate_environment(self) -> Self:
         """Validate that api key and python package exists in environment."""
diff --git a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
index cc03698e5ef93..c6065a137e5c7 100644
--- a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
+++ b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
@@ -35,6 +35,13 @@ def test_openai_model_param() -> None:
     assert llm.model_name == "foo"
 
 
+def test_openai_o1_temperature() -> None:
+    llm = ChatOpenAI(model="o1-preview")
+    assert llm.temperature == 1
+    llm = ChatOpenAI(model_name="o1-mini")  # type: ignore[call-arg]
+    assert llm.temperature == 1
+
+
 def test_function_message_dict_to_function_message() -> None:
     content = json.dumps({"result": "Example #1"})
     name = "test_function"