diff --git a/litellm/integrations/langfuse/langfuse_otel_attributes.py b/litellm/integrations/langfuse/langfuse_otel_attributes.py
index fb4a0a6a36c..89171b5cb40 100644
--- a/litellm/integrations/langfuse/langfuse_otel_attributes.py
+++ b/litellm/integrations/langfuse/langfuse_otel_attributes.py
@@ -14,6 +14,7 @@ from litellm.integrations.opentelemetry_utils.base_otel_llm_obs_attributes impor
     BaseLLMObsOTELAttributes,
     safe_set_attribute,
 )
+from litellm.litellm_core_utils.safe_json_dumps import safe_dumps
 from litellm.types.llms.openai import HttpxBinaryResponseContent, ResponsesAPIResponse
 from litellm.types.utils import (
     EmbeddingResponse,
@@ -96,7 +97,7 @@ class LangfuseLLMObsOTELAttributes(BaseLLMObsOTELAttributes):
             prompt["tools"] = tools
 
         input = prompt
-        safe_set_attribute(span, "langfuse.observation.input", json.dumps(input))
+        safe_set_attribute(span, "langfuse.observation.input", safe_dumps(input))
 
     @staticmethod
     @override
diff --git a/tests/test_litellm/integrations/langfuse/test_langfuse_otel_attributes.py b/tests/test_litellm/integrations/langfuse/test_langfuse_otel_attributes.py
new file mode 100644
index 00000000000..79bdea366cf
--- /dev/null
+++ b/tests/test_litellm/integrations/langfuse/test_langfuse_otel_attributes.py
@@ -0,0 +1,98 @@
+"""
+Tests for LangfuseLLMObsOTELAttributes, specifically verifying that pydantic
+Message objects in the messages list are correctly serialized without raising
+TypeError. Regression test for:
+  https://github.com/BerriAI/litellm/issues/26977
+"""
+
+import json
+import os
+import sys
+from unittest.mock import MagicMock
+
+import pytest
+
+sys.path.insert(0, os.path.abspath("../../../.."))
+
+from litellm.integrations.langfuse.langfuse_otel_attributes import (
+    LangfuseLLMObsOTELAttributes,
+)
+from litellm.types.utils import Message
+
+
+def test_set_messages_with_pydantic_message_objects():
+    """
+    Regression test for issue #26977:
+    set_messages should not raise 'Object of type Message is not JSON serializable'
+    when messages is a list of litellm.Message (pydantic) objects.
+    """
+    span = MagicMock()
+    kwargs = {
+        "messages": [Message(role="user", content="hello")],
+        "optional_params": {},
+    }
+
+    # Should not raise TypeError
+    LangfuseLLMObsOTELAttributes.set_messages(span, kwargs)
+
+    # Verify that set_attribute was called with a valid JSON string
+    span.set_attribute.assert_called_once()
+    key, value = span.set_attribute.call_args[0]
+    assert key == "langfuse.observation.input"
+
+    # The value must be parseable JSON
+    parsed = json.loads(value)
+    assert "messages" in parsed
+    assert parsed["messages"][0]["role"] == "user"
+    assert parsed["messages"][0]["content"] == "hello"
+
+
+def test_set_messages_with_dict_messages():
+    """
+    Ensure that plain dict messages still work correctly after the fix.
+    """
+    span = MagicMock()
+    kwargs = {
+        "messages": [{"role": "user", "content": "hello"}],
+        "optional_params": {},
+    }
+
+    LangfuseLLMObsOTELAttributes.set_messages(span, kwargs)
+
+    span.set_attribute.assert_called_once()
+    key, value = span.set_attribute.call_args[0]
+    assert key == "langfuse.observation.input"
+
+    parsed = json.loads(value)
+    assert parsed["messages"][0]["role"] == "user"
+
+
+def test_set_messages_with_tools():
+    """
+    Ensure tools are included in the serialized input and pydantic messages
+    are handled correctly together.
+    """
+    span = MagicMock()
+    kwargs = {
+        "messages": [Message(role="user", content="what's the weather?")],
+        "optional_params": {
+            "tools": [
+                {
+                    "type": "function",
+                    "function": {
+                        "name": "get_weather",
+                        "parameters": {"type": "object"},
+                    },
+                }
+            ]
+        },
+    }
+
+    LangfuseLLMObsOTELAttributes.set_messages(span, kwargs)
+
+    span.set_attribute.assert_called_once()
+    key, value = span.set_attribute.call_args[0]
+    parsed = json.loads(value)
+    assert "tools" in parsed
+    assert parsed["tools"][0]["function"]["name"] == "get_weather"
+    assert parsed["messages"][0]["role"] == "user"