diff --git a/docs/en-US/component/message-box.md b/docs/en-US/component/message-box.md
index d9f07bf8e8..b4749e6bce 100644
--- a/docs/en-US/component/message-box.md
+++ b/docs/en-US/component/message-box.md
@@ -168,6 +168,7 @@ The corresponding methods are: `ElMessageBox`, `ElMessageBox.alert`, `ElMessageB
 | icon                              | custom icon component, overrides `type`                                                                                                  | ^[string] / ^[Component]                                                           | ''                                               |
 | customClass                       | custom class name for MessageBox                                                                                                         | ^[string]                                                                          | ''                                               |
 | customStyle                       | custom inline style for MessageBox                                                                                                       | ^[CSSProperties]                                                                   | {}                                               |
+| modalClass                        | custom class names for mask                                                                                                              | string                                                                             | —                                                |
 | callback                          | MessageBox closing callback if you don't prefer Promise                                                                                  | ^[Function]`(value: string, action: Action) => any \| (action: Action) => any`     | null                                             |
 | showClose                         | whether to show close icon of MessageBox                                                                                                 | ^[boolean]                                                                         | true                                             |
 | beforeClose                       | callback before MessageBox closes, and it will prevent MessageBox from closing                                                           | ^[Function]`(action: Action, instance: MessageBoxState, done: () => void) => void` | null                                             |