diff --git a/python/sglang/srt/managers/request_metrics_exporter.py b/python/sglang/srt/managers/request_metrics_exporter.py
index 2ecc655b7..ca4db1a9b 100644
--- a/python/sglang/srt/managers/request_metrics_exporter.py
+++ b/python/sglang/srt/managers/request_metrics_exporter.py
@@ -87,6 +87,7 @@ class FileRequestMetricsExporter(RequestMetricsExporter):
 
         # File handler state management
         self._current_file_handler = None
+        self._current_file_lock = asyncio.Lock()
         self._current_hour_suffix = None
 
     def _ensure_file_handler(self, hour_suffix: str):
@@ -135,20 +136,21 @@ class FileRequestMetricsExporter(RequestMetricsExporter):
             current_time = datetime.now()
             hour_suffix = current_time.strftime("%Y%m%d_%H")
 
-            # Ensure correct file handler is open for current hour
-            self._ensure_file_handler(hour_suffix)
+            async with self._current_file_lock:
+                # Ensure correct file handler is open for current hour
+                self._ensure_file_handler(hour_suffix)
 
-            if self._current_file_handler is None:
-                return
+                if self._current_file_handler is None:
+                    return
 
-            metrics_data = self._format_output_data(obj, out_dict)
+                metrics_data = self._format_output_data(obj, out_dict)
 
-            def write_file():
-                json.dump(metrics_data, self._current_file_handler)
-                self._current_file_handler.write("\n")
-                self._current_file_handler.flush()
+                def write_file():
+                    json.dump(metrics_data, self._current_file_handler)
+                    self._current_file_handler.write("\n")
+                    self._current_file_handler.flush()
 
-            await asyncio.to_thread(write_file)
+                await asyncio.to_thread(write_file)
         except Exception as e:
             logger.exception(f"Failed to write perf metrics to file: {e}")