All the validation rules you defined in a validation.xml file will apply to both client-side and server-side validation. Even when client-side validation is turned on, Struts Still does Server-side validation. There's nothing you have to do to turn that on. It's done automatically. All you have to do is make sure your ActionForm extends ValidatorForm and add an <html:errors /> tag to your JSP so that there is a place for server-side errors to be displayed.