diff --git a/optuna_dashboard/_cached_extra_study_property.py b/optuna_dashboard/_cached_extra_study_property.py
index 1e9de3fc..4395dad3 100644
--- a/optuna_dashboard/_cached_extra_study_property.py
+++ b/optuna_dashboard/_cached_extra_study_property.py
@@ -21,7 +21,7 @@ cached_extra_study_property_cache: Dict[int, "_CachedExtraStudyProperty"] = {}
 
 def get_cached_extra_study_property(
     study_id: int, trials: List[FrozenTrial]
-) -> Tuple[SearchSpaceListT, SearchSpaceListT, List[str], bool]:
+) -> Tuple[SearchSpaceListT, SearchSpaceListT, List[Tuple[str, bool]], bool]:
     with cached_extra_study_property_cache_lock:
         cached_extra_study_property = cached_extra_study_property_cache.get(study_id, None)
         if cached_extra_study_property is None:
@@ -43,7 +43,7 @@ class _CachedExtraStudyProperty:
         # union_user_attrs.
         self._intersection: Optional[SearchSpaceSetT] = None
         self._union: SearchSpaceSetT = set()
-        self._union_user_attrs: Set[str] = set()
+        self._union_user_attrs: Dict[str, bool] = {}  # attr_name: is_sortable (= is_number)
         self.has_intermediate_values: bool = False
 
     @property
@@ -61,9 +61,9 @@ class _CachedExtraStudyProperty:
         return union
 
     @property
-    def union_user_attrs(self) -> List[str]:
-        union = list(self._union_user_attrs)
-        union.sort()
+    def union_user_attrs(self) -> List[Tuple[str, bool]]:
+        union = [(name, is_sortable) for name, is_sortable in self._union_user_attrs.items()]
+        sorted(union, key=lambda x: x[0])
         return union
 
     def update(self, trials: List[FrozenTrial]) -> None:
@@ -75,20 +75,27 @@ class _CachedExtraStudyProperty:
             if not trial.state.is_finished():
                 next_cursor = trial.number
 
-            current_user_attrs = set(n for n in trial.user_attrs.keys())
-            self._union_user_attrs = self._union_user_attrs.union(current_user_attrs)
-            if trial.state == TrialState.FAIL:
-                continue
-
-            if not self.has_intermediate_values and len(trial.intermediate_values) > 0:
-                self.has_intermediate_values = True
-
-            current = set([(n, d) for n, d in trial.distributions.items()])
-            self._union = self._union.union(current)
-
-            if self._intersection is None:
-                self._intersection = copy.copy(current)
-            else:
-                self._intersection = self._intersection.intersection(current)
+            self._update_user_attrs(trial)
+            if trial.state != TrialState.FAIL:
+                self._update_intermediate_values(trial)
+                self._update_search_space(trial)
 
         self._cursor = next_cursor
+
+    def _update_user_attrs(self, trial: FrozenTrial) -> None:
+        # TODO(c-bata): Support numpy-specific number types.
+        current_user_attrs = {k: isinstance(v, (int, float)) for k, v in trial.user_attrs.items()}
+        self._union_user_attrs.update(current_user_attrs)
+
+    def _update_intermediate_values(self, trial: FrozenTrial) -> None:
+        if not self.has_intermediate_values and len(trial.intermediate_values) > 0:
+            self.has_intermediate_values = True
+
+    def _update_search_space(self, trial: FrozenTrial) -> None:
+        current = set([(n, d) for n, d in trial.distributions.items()])
+        self._union = self._union.union(current)
+
+        if self._intersection is None:
+            self._intersection = copy.copy(current)
+        else:
+            self._intersection = self._intersection.intersection(current)
diff --git a/optuna_dashboard/_serializer.py b/optuna_dashboard/_serializer.py
index 9dca618e..5ed4a027 100644
--- a/optuna_dashboard/_serializer.py
+++ b/optuna_dashboard/_serializer.py
@@ -29,6 +29,13 @@ Attribute = TypedDict(
         "value": str,
     },
 )
+AttributeSpec = TypedDict(
+    "AttributeSpec",
+    {
+        "key": str,
+        "sortable": bool,
+    },
+)
 IntermediateValue = TypedDict(
     "IntermediateValue",
     {
@@ -71,7 +78,7 @@ def serialize_study_detail(
     trials: List[FrozenTrial],
     intersection: List[Tuple[str, BaseDistribution]],
     union: List[Tuple[str, BaseDistribution]],
-    union_user_attrs: List[str],
+    union_user_attrs: List[Tuple[str, bool]],
     has_intermediate_values: bool,
 ) -> Dict[str, Any]:
     serialized: Dict[str, Any] = {
@@ -84,7 +91,7 @@ def serialize_study_detail(
     serialized["trials"] = [serialize_frozen_trial(summary._study_id, trial) for trial in trials]
     serialized["intersection_search_space"] = serialize_search_space(intersection)
     serialized["union_search_space"] = serialize_search_space(union)
-    serialized["union_user_attrs"] = union_user_attrs
+    serialized["union_user_attrs"] = [{"key": a[0], "sortable": a[1]} for a in union_user_attrs]
     serialized["has_intermediate_values"] = has_intermediate_values
     serialized["note"] = note.get_note_from_system_attrs(summary.system_attrs)
     return serialized
diff --git a/optuna_dashboard/ts/apiClient.ts b/optuna_dashboard/ts/apiClient.ts
index 2f00395b..a539c590 100644
--- a/optuna_dashboard/ts/apiClient.ts
+++ b/optuna_dashboard/ts/apiClient.ts
@@ -44,7 +44,7 @@ interface StudyDetailResponse {
   trials: TrialResponse[]
   intersection_search_space: SearchSpace[]
   union_search_space: SearchSpace[]
-  union_user_attrs: string[]
+  union_user_attrs: AttributeSpec[]
   has_intermediate_values: boolean
   note: {
     version: number
diff --git a/optuna_dashboard/ts/components/TrialTable.tsx b/optuna_dashboard/ts/components/TrialTable.tsx
index 6763323c..d46c93f1 100644
--- a/optuna_dashboard/ts/components/TrialTable.tsx
+++ b/optuna_dashboard/ts/components/TrialTable.tsx
@@ -165,21 +165,21 @@ export const TrialTable: FC<{ studyDetail: StudyDetail | null }> = ({
     })
   }
 
-  studyDetail?.union_user_attrs.forEach((attr_name) => {
+  studyDetail?.union_user_attrs.forEach((attr_spec) => {
     columns.push({
       field: "user_attrs",
-      label: `User attribute ${attr_name}`,
+      label: `User attribute ${attr_spec.key}`,
       toCellValue: (i) =>
-        trials[i].user_attrs.find((attr) => attr.key === attr_name)?.value ||
-        null,
-      sortable: true,
-      filterable: true,
+        trials[i].user_attrs.find((attr) => attr.key === attr_spec.key)
+          ?.value || null,
+      sortable: attr_spec.sortable,
+      filterable: !attr_spec.sortable,
       less: (firstEl, secondEl): number => {
         const firstVal = firstEl.user_attrs.find(
-          (attr) => attr.key === attr_name
+          (attr) => attr.key === attr_spec.key
         )?.value
         const secondVal = secondEl.user_attrs.find(
-          (attr) => attr.key === attr_name
+          (attr) => attr.key === attr_spec.key
         )?.value
 
         if (firstVal === secondVal) {
diff --git a/optuna_dashboard/ts/types/index.d.ts b/optuna_dashboard/ts/types/index.d.ts
index 372f7a5f..6541a93b 100644
--- a/optuna_dashboard/ts/types/index.d.ts
+++ b/optuna_dashboard/ts/types/index.d.ts
@@ -58,6 +58,11 @@ declare interface Attribute {
   value: string
 }
 
+declare interface AttributeSpec {
+  key: string
+  sortable: boolean
+}
+
 declare interface Note {
   version: number
   body: string
@@ -95,7 +100,7 @@ declare interface StudyDetail {
   trials: Trial[]
   intersection_search_space: SearchSpace[]
   union_search_space: SearchSpace[]
-  union_user_attrs: string[]
+  union_user_attrs: AttributeSpec[]
   has_intermediate_values: boolean
   note: Note
 }
diff --git a/typescript_tests/TrialTable.test.tsx b/typescript_tests/TrialTable.test.tsx
index 8e87b5d8..da9bdeca 100644
--- a/typescript_tests/TrialTable.test.tsx
+++ b/typescript_tests/TrialTable.test.tsx
@@ -74,7 +74,10 @@ const studyDetail = {
       attributes: { low: -3, high: 3 },
     },
   ],
-  union_user_attrs: ["foo", "bar"],
+  union_user_attrs: [
+    { key: "foo", sortable: false },
+    { key: "bar", sortable: false },
+  ],
   has_intermediate_values: false,
   note: {
     version: 0,