diff --git a/plugins/baser-core/src/Model/Validation/BcValidation.php b/plugins/baser-core/src/Model/Validation/BcValidation.php
index 8e471daa86..f32e673a4c 100644
--- a/plugins/baser-core/src/Model/Validation/BcValidation.php
+++ b/plugins/baser-core/src/Model/Validation/BcValidation.php
@@ -583,4 +583,20 @@ public static function reserved($value): bool
         return true;
     }
 
+    /**
+     * 選択リストに同じ項目を複数登録するかをチェック
+     *
+     * @param $value
+     * @return bool
+     * @checked
+     * @notodo
+     * @unitTest
+     */
+    public static function checkSelectList($value): bool
+    {
+        $data = preg_split("/\r\n|\n|\r/", $value);
+        $result = max(array_count_values($data));
+        return ($result < 2);
+    }
+
 }
diff --git a/plugins/baser-core/tests/TestCase/Model/Validation/BcValidationTest.php b/plugins/baser-core/tests/TestCase/Model/Validation/BcValidationTest.php
index 8f33070ca2..f41450c54d 100644
--- a/plugins/baser-core/tests/TestCase/Model/Validation/BcValidationTest.php
+++ b/plugins/baser-core/tests/TestCase/Model/Validation/BcValidationTest.php
@@ -584,4 +584,20 @@ public function testCheckHiragana()
         $this->assertEquals($result, false);
     }
 
+    /**
+     * test checkSelectList
+     */
+    public function test_checkSelectList()
+    {
+        //戻り＝falseケース
+        $str = "あ\rべ\r\nあ\nべ\ntest";
+        $result = $this->BcValidation->checkSelectList($str);
+        $this->assertFalse($result);
+        //戻り＝trueケース
+        $str = "あa\nべ\nあ";
+        $result = $this->BcValidation->checkSelectList($str);
+        $this->assertTrue($result);
+    }
+
+
 }
diff --git a/plugins/bc-custom-content/src/Model/Table/CustomFieldsTable.php b/plugins/bc-custom-content/src/Model/Table/CustomFieldsTable.php
index 2cb17867d8..c7bdbdc684 100644
--- a/plugins/bc-custom-content/src/Model/Table/CustomFieldsTable.php
+++ b/plugins/bc-custom-content/src/Model/Table/CustomFieldsTable.php
@@ -72,6 +72,14 @@ public function validationDefault(Validator $validator): Validator
         $validator
             ->scalar('type')
             ->notEmptyString('type', __d('baser_core', 'タイプを入力してください。'));
+        $validator
+            ->add('source', [
+                'checkSelectList' => [
+                    'provider' => 'bc',
+                    'rule' => ['checkSelectList'],
+                    'message' => __d('baser_core', '選択リストに同じ項目を複数登録できません。')
+                ]
+        ]);
         return $validator;
     }