diff --git a/python/packages/openai/agent_framework_openai/_chat_completion_client.py b/python/packages/openai/agent_framework_openai/_chat_completion_client.py
index d64933fae8..fee47e54da 100644
--- a/python/packages/openai/agent_framework_openai/_chat_completion_client.py
+++ b/python/packages/openai/agent_framework_openai/_chat_completion_client.py
@@ -85,6 +85,14 @@
 
 logger = logging.getLogger("agent_framework.openai")
 
+# Error message shared with tests — extracted to a constant to keep the
+# implementation and its assertions in sync.
+_AZURE_WEB_SEARCH_UNSUPPORTED_MSG = (
+    "Web search is not supported by the Azure OpenAI Chat Completions API. "
+    "Use agent_framework.openai.OpenAIChatClient (Responses API) for "
+    "web search support on Azure."
+)
+
 DEFAULT_AZURE_OPENAI_CHAT_COMPLETION_API_VERSION = "2024-12-01-preview"
 
 ResponseModelBoundT = TypeVar("ResponseModelBoundT", bound=BaseModel)
@@ -373,6 +381,7 @@ def __init__(
         else:
             self.default_headers = None
         self.instruction_role = instruction_role
+        self._use_azure_client = use_azure_client
         if use_azure_client:
             self.OTEL_PROVIDER_NAME = "azure.ai.openai"  # type: ignore[misc]
 
@@ -589,6 +598,12 @@ def _prepare_tools_for_openai(
         Converts FunctionTool to JSON schema format. Web search tools are routed
         to web_search_options parameter. All other tools pass through unchanged.
 
+        Note:
+            Azure OpenAI Chat Completions API does not support ``web_search_options``.
+            When configured with an Azure endpoint, passing web search tools raises
+            :class:`ValueError`. Use :class:`~agent_framework.openai.OpenAIChatClient`
+            (Responses API) for web search support on Azure.
+
         Args:
             tools: Tool(s) to prepare.
 
@@ -603,6 +618,8 @@ def _prepare_tools_for_openai(
             elif isinstance(tool, MutableMapping):
                 typed_tool = cast(MutableMapping[str, Any], tool)
                 if typed_tool.get("type") == "web_search":
+                    if self._use_azure_client:
+                        raise ValueError(_AZURE_WEB_SEARCH_UNSUPPORTED_MSG)
                     # Web search is handled via web_search_options, not tools array
                     web_search_options = {k: v for k, v in typed_tool.items() if k != "type"}
                 else:
diff --git a/python/packages/openai/tests/openai/test_openai_chat_completion_client.py b/python/packages/openai/tests/openai/test_openai_chat_completion_client.py
index 2489eeaf23..8183678a5c 100644
--- a/python/packages/openai/tests/openai/test_openai_chat_completion_client.py
+++ b/python/packages/openai/tests/openai/test_openai_chat_completion_client.py
@@ -3,6 +3,7 @@
 import inspect
 import json
 import os
+import re
 from typing import Any, cast
 from unittest.mock import MagicMock, patch
 
@@ -28,6 +29,9 @@
 from pytest import param
 
 from agent_framework_openai import OpenAIChatCompletionClient, RawOpenAIChatCompletionClient
+from agent_framework_openai._chat_completion_client import (
+    _AZURE_WEB_SEARCH_UNSUPPORTED_MSG,
+)
 from agent_framework_openai._exceptions import OpenAIContentFilterException
 
 skip_if_openai_integration_tests_disabled = pytest.mark.skipif(
@@ -1252,6 +1256,39 @@ def test_prepare_tools_with_web_search_no_location(
     assert result["web_search_options"] == {}
 
 
+def test_prepare_tools_with_web_search_on_azure_raises(
+    openai_unit_test_env: dict[str, str],
+) -> None:
+    """Test that web search raises ValueError when configured with Azure endpoint."""
+    client = OpenAIChatCompletionClient(
+        azure_endpoint="https://test.openai.azure.com",
+        model="gpt-4o-mini",
+        api_key="test-key",
+    )
+
+    web_search_tool = OpenAIChatCompletionClient.get_web_search_tool()
+
+    with pytest.raises(
+        ValueError,
+        match=re.escape(_AZURE_WEB_SEARCH_UNSUPPORTED_MSG),
+    ):
+        client._prepare_tools_for_openai([web_search_tool])
+
+
+def test_prepare_tools_with_web_search_on_openai_allowed(
+    openai_unit_test_env: dict[str, str],
+) -> None:
+    """Test that web search works normally on non-Azure client."""
+    client = OpenAIChatCompletionClient()
+
+    web_search_tool = OpenAIChatCompletionClient.get_web_search_tool()
+
+    result = client._prepare_tools_for_openai([web_search_tool])
+
+    # Non-Azure client should include web_search_options
+    assert "web_search_options" in result
+
+
 def test_prepare_options_with_instructions(
     openai_unit_test_env: dict[str, str],
 ) -> None: