diff --git a/litellm/llms/groq/chat/transformation.py b/litellm/llms/groq/chat/transformation.py
index a75ecd8cc7..34ea7b03dd 100644
--- a/litellm/llms/groq/chat/transformation.py
+++ b/litellm/llms/groq/chat/transformation.py
@@ -323,4 +323,12 @@ class GroqChatCompletionStreamingHandler(OpenAIChatCompletionStreamingHandler):
                 status_code=error.get("code"), message=error.get("message"), body=error
             )
 
+        # Map Groq's 'reasoning' field to LiteLLM's 'reasoning_content' field
+        # Groq returns delta.reasoning, but LiteLLM expects delta.reasoning_content
+        choices = chunk.get("choices", [])
+        for choice in choices:
+            delta = choice.get("delta", {})
+            if "reasoning" in delta:
+                delta["reasoning_content"] = delta.pop("reasoning")
+
         return super().chunk_parser(chunk)
diff --git a/tests/llm_translation/test_groq.py b/tests/llm_translation/test_groq.py
index 33c1a42587..b82cffd418 100644
--- a/tests/llm_translation/test_groq.py
+++ b/tests/llm_translation/test_groq.py
@@ -11,7 +11,10 @@ import pytest
 
 import litellm
 from base_llm_unit_tests import BaseLLMChatTest
-from litellm.llms.groq.chat.transformation import GroqChatConfig
+from litellm.llms.groq.chat.transformation import (
+    GroqChatConfig,
+    GroqChatCompletionStreamingHandler,
+)
 
 class TestGroq(BaseLLMChatTest):
     def get_base_completion_call_args(self) -> dict:
@@ -164,3 +167,124 @@ class TestGroqStructuredOutputs:
         if "tools" in result:
             tool_names = [t.get("function", {}).get("name") for t in result["tools"]]
             assert "json_tool_call" not in tool_names
+
+
+class TestGroqReasoning:
+    """
+    Tests for Groq reasoning field mapping.
+    
+    Groq returns 'reasoning' field in delta, but LiteLLM expects 'reasoning_content'.
+    """
+
+    def test_reasoning_field_mapping_in_streaming_chunks(self):
+        """
+        Test that Groq's 'reasoning' field in streaming chunks is properly mapped
+        to LiteLLM's 'reasoning_content' field.
+        """
+        handler = GroqChatCompletionStreamingHandler(
+            streaming_response=None, sync_stream=True
+        )
+
+        # Simulate a chunk with reasoning field as returned by Groq
+        groq_chunk = {
+            "id": "chatcmpl-test",
+            "object": "chat.completion.chunk",
+            "created": 1769511767,
+            "model": "qwen/qwen3-32b",
+            "choices": [
+                {
+                    "delta": {
+                        "reasoning": "This is reasoning content",
+                        "role": None,
+                    },
+                    "finish_reason": None,
+                    "index": 0,
+                }
+            ],
+        }
+
+        # Parse the chunk
+        parsed_chunk = handler.chunk_parser(groq_chunk)
+
+        # Verify that reasoning was mapped to reasoning_content
+        assert parsed_chunk.choices[0].delta.reasoning_content == "This is reasoning content"
+        # Verify that the original 'reasoning' field was removed
+        assert not hasattr(parsed_chunk.choices[0].delta, "reasoning")
+
+    def test_reasoning_field_not_present(self):
+        """
+        Test that chunks without reasoning field still work correctly.
+        """
+        handler = GroqChatCompletionStreamingHandler(
+            streaming_response=None, sync_stream=True
+        )
+
+        # Simulate a chunk without reasoning field
+        groq_chunk = {
+            "id": "chatcmpl-test",
+            "object": "chat.completion.chunk",
+            "created": 1769511767,
+            "model": "qwen/qwen3-32b",
+            "choices": [
+                {
+                    "delta": {
+                        "content": "Regular content",
+                        "role": "assistant",
+                    },
+                    "finish_reason": None,
+                    "index": 0,
+                }
+            ],
+        }
+
+        # Parse the chunk
+        parsed_chunk = handler.chunk_parser(groq_chunk)
+
+        # Verify that content is present
+        assert parsed_chunk.choices[0].delta.content == "Regular content"
+        assert parsed_chunk.choices[0].delta.role == "assistant"
+        # Verify that reasoning_content is not set (it should be deleted by Delta.__init__)
+        assert not hasattr(parsed_chunk.choices[0].delta, "reasoning_content")
+
+    def test_reasoning_with_tool_calls(self):
+        """
+        Test that reasoning field is properly mapped even when tool_calls are present.
+        """
+        handler = GroqChatCompletionStreamingHandler(
+            streaming_response=None, sync_stream=True
+        )
+
+        # Simulate a chunk with both reasoning and tool_calls
+        groq_chunk = {
+            "id": "chatcmpl-test",
+            "object": "chat.completion.chunk",
+            "created": 1769511767,
+            "model": "qwen/qwen3-32b",
+            "choices": [
+                {
+                    "delta": {
+                        "reasoning": "Reasoning before tool call",
+                        "tool_calls": [
+                            {
+                                "index": 0,
+                                "id": "call_123",
+                                "function": {"name": "test_function", "arguments": "{}"},
+                                "type": "function",
+                            }
+                        ],
+                    },
+                    "finish_reason": None,
+                    "index": 0,
+                }
+            ],
+        }
+
+        # Parse the chunk
+        parsed_chunk = handler.chunk_parser(groq_chunk)
+
+        # Verify that reasoning was mapped to reasoning_content
+        assert parsed_chunk.choices[0].delta.reasoning_content == "Reasoning before tool call"
+        # Verify tool_calls are still present
+        assert parsed_chunk.choices[0].delta.tool_calls is not None
+        assert len(parsed_chunk.choices[0].delta.tool_calls) == 1
+        assert parsed_chunk.choices[0].delta.tool_calls[0]["function"]["name"] == "test_function"