diff --git a/plugins/observability/langfuse/__init__.py b/plugins/observability/langfuse/__init__.py
index a18ebf98fc9..b992484b05e 100644
--- a/plugins/observability/langfuse/__init__.py
+++ b/plugins/observability/langfuse/__init__.py
@@ -227,7 +227,30 @@ def _trace_key(task_id: str, session_id: str) -> str:
     return f"thread:{threading.get_ident()}"
 
 
-def _truncate_text(value: str, max_chars: int) -> str:
+def _is_base64_data_uri(value: str) -> bool:
+    prefix = value[:200].lower()
+    return prefix.startswith("data:") and ";base64," in prefix
+
+
+def _redact_data_uri(value: str) -> dict[str, Any]:
+    header = value.split(",", 1)[0] if "," in value else "data:"
+    media_type = header[5:].split(";", 1)[0] if header.startswith("data:") else ""
+    return {
+        "type": "data_uri",
+        "media_type": media_type or None,
+        "omitted": True,
+        "length": len(value),
+    }
+
+
+def _truncate_text(value: str, max_chars: int) -> Any:
+    # Langfuse SDK treats data:*;base64 strings as media and attempts to
+    # decode them. Truncating those strings produces invalid base64 and noisy
+    # "Error parsing base64 data URI" logs. Observability only needs metadata,
+    # not raw image/audio payloads, so redact the whole data URI before it
+    # reaches the SDK.
+    if _is_base64_data_uri(value):
+        return _redact_data_uri(value)
     if len(value) <= max_chars:
         return value
     return value[:max_chars] + f"... [truncated {len(value) - max_chars} chars]"
diff --git a/tests/plugins/test_langfuse_plugin.py b/tests/plugins/test_langfuse_plugin.py
index 51c8c3f4635..ca91feae613 100644
--- a/tests/plugins/test_langfuse_plugin.py
+++ b/tests/plugins/test_langfuse_plugin.py
@@ -171,6 +171,40 @@ class TestHooksInert:
         mod.on_post_tool_call(tool_name="read_file", args={}, result="ok", task_id="t", session_id="s")
 
 
+class TestPayloadSanitization:
+    def test_safe_value_redacts_base64_data_uri_instead_of_truncating(self):
+        sys.modules.pop("plugins.observability.langfuse", None)
+        import importlib
+        mod = importlib.import_module("plugins.observability.langfuse")
+
+        payload = "data:image/png;base64," + ("a" * 20000)
+        result = mod._safe_value(payload)
+
+        assert result == {
+            "type": "data_uri",
+            "media_type": "image/png",
+            "omitted": True,
+            "length": len(payload),
+        }
+
+    def test_serialize_messages_redacts_data_uri_parts(self):
+        sys.modules.pop("plugins.observability.langfuse", None)
+        import importlib
+        mod = importlib.import_module("plugins.observability.langfuse")
+
+        payload = "data:image/jpeg;base64," + ("b" * 20000)
+        serialized = mod._serialize_messages([
+            {"role": "user", "content": [{"type": "image_url", "image_url": {"url": payload}}]}
+        ])
+
+        assert serialized[0]["content"][0]["image_url"]["url"] == {
+            "type": "data_uri",
+            "media_type": "image/jpeg",
+            "omitted": True,
+            "length": len(payload),
+        }
+
+
 # ---------------------------------------------------------------------------
 # Placeholder-credential guard (#23823).
 #