$('#form').validator({ custom: { 'ppolicy': function($el) { var $ret = 'PPolicy error'; $.ajax({ url: '/checkppolicy', dataType: 'json', async: false, data: 'pwd=' + $el.val(), success: function(data) { $ret = data; } }); this.options.errors['ppolicy'] = $ret['reason']; return $ret['match']; } }, errors: { 'ppolicy': 'PPolicy error', } })