diff --git a/optuna_dashboard/serializer.py b/optuna_dashboard/serializer.py
index ce407f52..b113f515 100644
--- a/optuna_dashboard/serializer.py
+++ b/optuna_dashboard/serializer.py
@@ -1,3 +1,4 @@
+import json
 from typing import Any
 from typing import Dict
 from typing import List
@@ -14,7 +15,7 @@ except ImportError:
     from typing_extensions import TypedDict
 
 
-MAX_ATTR_LENGTH = 128
+MAX_ATTR_LENGTH = 1024
 Attribute = TypedDict(
     "Attribute",
     {
@@ -42,16 +43,11 @@ def serialize_attrs(attrs: Dict[str, Any]) -> List[Attribute]:
     serialized: List[Attribute] = []
     for k, v in attrs.items():
         value: str
-        if isinstance(v, str):
-            value = v[:MAX_ATTR_LENGTH] if len(v) > MAX_ATTR_LENGTH else v
-        elif isinstance(v, (bool, float, int)):
-            value = str(v)
-        elif isinstance(v, bytes):
+        if isinstance(v, bytes):
             value = "<binary object>"
-        elif v is None:
-            value = "None"
-        else:  # unsupported type
-            continue
+        else:
+            value = json.dumps(v)
+            value = value[:MAX_ATTR_LENGTH] if len(value) > MAX_ATTR_LENGTH else value
         serialized.append({"key": k, "value": value})
     return serialized
 
diff --git a/tests/test_serializers.py b/tests/test_serializers.py
index 1137d9e2..c7e70f17 100644
--- a/tests/test_serializers.py
+++ b/tests/test_serializers.py
@@ -9,7 +9,7 @@ class SerializeAttrsTestCase(TestCase):
         self.assertEqual(serialized[0]["value"], "<binary object>")
 
     def test_serialize_string(self) -> None:
-        for length in [100, 128, 150]:
+        for length in [1000, 1024, 1100]:
             with self.subTest(f"length: {length}"):
                 value = "a" * length
                 serialized = serialize_attrs(
@@ -17,4 +17,12 @@ class SerializeAttrsTestCase(TestCase):
                         "key": value,
                     }
                 )
-                self.assertLessEqual(len(serialized[0]["value"]), 128)
+                self.assertLessEqual(len(serialized[0]["value"]), 1024)
+
+    def test_serialize_dict(self) -> None:
+        serialized = serialize_attrs(
+            {
+                "key": {"foo": "bar"},
+            }
+        )
+        self.assertLessEqual(len(serialized), 1)