diff --git a/core/src/main/java/com/scalar/db/storage/jdbc/JdbcUtils.java b/core/src/main/java/com/scalar/db/storage/jdbc/JdbcUtils.java
index feab4e014..584c22ae6 100644
--- a/core/src/main/java/com/scalar/db/storage/jdbc/JdbcUtils.java
+++ b/core/src/main/java/com/scalar/db/storage/jdbc/JdbcUtils.java
@@ -36,8 +36,6 @@ public static BasicDataSource initDataSource(
     if (transactional) {
       dataSource.setDefaultAutoCommit(false);
       dataSource.setAutoCommitOnReturn(false);
-      // if transactional, the default isolation level is SERIALIZABLE
-      dataSource.setDefaultTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);
     }
 
     config