diff --git a/vllm/entrypoints/openai/chat_completion/protocol.py b/vllm/entrypoints/openai/chat_completion/protocol.py
index 9763f2e5c..1bf0de53f 100644
--- a/vllm/entrypoints/openai/chat_completion/protocol.py
+++ b/vllm/entrypoints/openai/chat_completion/protocol.py
@@ -555,8 +555,16 @@ class ChatCompletionRequest(OpenAIBaseModel):
             return data
 
         structured_outputs_kwargs = data["structured_outputs"]
+        # structured_outputs may arrive as a dict (from JSON/raw kwargs) or
+        # as a StructuredOutputsParams dataclass instance.
+        is_dataclass = isinstance(structured_outputs_kwargs, StructuredOutputsParams)
         count = sum(
-            structured_outputs_kwargs.get(k) is not None
+            (
+                getattr(structured_outputs_kwargs, k, None)
+                if is_dataclass
+                else structured_outputs_kwargs.get(k)
+            )
+            is not None
             for k in ("json", "regex", "choice")
         )
         # you can only use one kind of constraints for structured outputs
diff --git a/vllm/entrypoints/openai/completion/protocol.py b/vllm/entrypoints/openai/completion/protocol.py
index 531de984b..226dd6c1a 100644
--- a/vllm/entrypoints/openai/completion/protocol.py
+++ b/vllm/entrypoints/openai/completion/protocol.py
@@ -320,8 +320,16 @@ class CompletionRequest(OpenAIBaseModel):
             return data
 
         structured_outputs_kwargs = data["structured_outputs"]
+        # structured_outputs may arrive as a dict (from JSON/raw kwargs) or
+        # as a StructuredOutputsParams dataclass instance.
+        is_dataclass = isinstance(structured_outputs_kwargs, StructuredOutputsParams)
         count = sum(
-            structured_outputs_kwargs.get(k) is not None
+            (
+                getattr(structured_outputs_kwargs, k, None)
+                if is_dataclass
+                else structured_outputs_kwargs.get(k)
+            )
+            is not None
             for k in ("json", "regex", "choice")
         )
         if count > 1: