diff --git a/langfuse/_client/attributes.py b/langfuse/_client/attributes.py
index 5ae81000c..9bd01c44e 100644
--- a/langfuse/_client/attributes.py
+++ b/langfuse/_client/attributes.py
@@ -164,7 +164,7 @@ def _serialize(obj: Any) -> Optional[str]:
     if obj is None or isinstance(obj, str):
         return obj
 
-    return json.dumps(obj, cls=EventSerializer)
+    return json.dumps(obj, cls=EventSerializer, ensure_ascii=False)
 
 
 def _flatten_and_serialize_metadata(
diff --git a/langfuse/_task_manager/score_ingestion_consumer.py b/langfuse/_task_manager/score_ingestion_consumer.py
index 1a5b61f91..7ad781be0 100644
--- a/langfuse/_task_manager/score_ingestion_consumer.py
+++ b/langfuse/_task_manager/score_ingestion_consumer.py
@@ -85,7 +85,7 @@ def _next(self) -> list:
 
                 # check for serialization errors
                 try:
-                    json.dumps(event, cls=EventSerializer)
+                    json.dumps(event, cls=EventSerializer, ensure_ascii=False)
                 except Exception as e:
                     self._log.error(
                         f"Data error: Failed to serialize score object for ingestion. Score will be dropped. Error: {e}"
@@ -117,7 +117,7 @@ def _next(self) -> list:
 
     def _get_item_size(self, item: Any) -> int:
         """Return the size of the item in bytes."""
-        return len(json.dumps(item, cls=EventSerializer).encode())
+        return len(json.dumps(item, cls=EventSerializer, ensure_ascii=False).encode())
 
     def run(self) -> None:
         """Run the consumer."""
diff --git a/langfuse/_utils/request.py b/langfuse/_utils/request.py
index b106cee2f..a7be90f47 100644
--- a/langfuse/_utils/request.py
+++ b/langfuse/_utils/request.py
@@ -60,7 +60,7 @@ def post(self, **kwargs: Any) -> httpx.Response:
         """Post the `kwargs` to the API"""
         log = logging.getLogger("langfuse")
         url = self._remove_trailing_slash(self._base_url) + "/api/public/ingestion"
-        data = json.dumps(kwargs, cls=EventSerializer)
+        data = json.dumps(kwargs, cls=EventSerializer, ensure_ascii=False)
         log.debug("making request: %s to %s", data, url)
         headers = self.generate_headers()
         res = self._session.post(
diff --git a/tests/test_unicode_serialization.py b/tests/test_unicode_serialization.py
new file mode 100644
index 000000000..9c9080390
--- /dev/null
+++ b/tests/test_unicode_serialization.py
@@ -0,0 +1,20 @@
+"""Test Unicode character handling in serialization."""
+
+from langfuse._client.attributes import _serialize
+
+def test_mixed_unicode_preserved():
+    """Test that mixed Unicode content is preserved."""
+    data = {
+        "japanese": "こんにちは",
+        "chinese": "你好",
+        "korean": "안녕하세요",
+        "arabic": "مرحبا",
+        "russian": "Привет",
+        "emoji": "Hello, 🌍!",
+    }
+    serialized = _serialize(data)
+    assert serialized is not None
+
+    assert "\\u" not in serialized, "Should not contain Unicode escapes"
+    for value in data.values():
+        assert value in serialized, f"Should contain {value}"