diff --git a/optuna_dashboard/_serializer.py b/optuna_dashboard/_serializer.py
index 9d2241be..d3cd786f 100644
--- a/optuna_dashboard/_serializer.py
+++ b/optuna_dashboard/_serializer.py
@@ -19,7 +19,6 @@ from ._preferential_history import _SYSTEM_ATTR_PREFIX_HISTORY
 from .artifact._backend import list_trial_artifacts
 from .preferential._study import _SYSTEM_ATTR_PREFERENTIAL_STUDY
 from .preferential._system_attrs import get_preferences
-from .preferential._system_attrs import get_skipped_trial_ids
 from .preferential._system_attrs import is_preference_removed