diff -u b/menu_attributes.module b/menu_attributes.module
--- b/menu_attributes.module
+++ b/menu_attributes.module
@@ -139,7 +139,7 @@
   $attributes = variable_get('menu_attributes_menus', array());
 
   // Set default attributes.
-  $default_attributes = !empty($attributes[$menu_name]) ? $attributes[$menu_name] : array('id' => '', 'class' => '');
+  $default_attributes = !empty($attributes[$menu_name]) ? $attributes[$menu_name] : array('id' => '', 'class' => 'menu');
 
   $form['attributes'] = array(
     '#type' => 'fieldset',
@@ -421,6 +421,7 @@
   $first_element_key = current(element_children($variables['tree']));
   $first_element = $variables['tree'][$first_element_key];
   $variables['menu_name'] = $first_element['#original_link']['menu_name'];
+  $variables['depth'] = $first_element['#original_link']['depth'];
 }
 
 /**
@@ -428,7 +429,10 @@
  */
 function menu_attributes_menu_tree($variables) {
   $menus = variable_get('menu_attributes_menus', array());
-  $attributes = !empty($menus[$variables['menu_name']]) ? array_filter($menus[$variables['menu_name']]) : array();
+  $attributes = array('class' => 'menu');
+  if (!empty($menus[$variables['menu_name']]) && $variables['depth'] == 1) {
+    $attributes = array_filter($menus[$variables['menu_name']]);
+  }
 
   return '<ul' . drupal_attributes($attributes) . '>' . $variables['tree'] . '</ul>';
 }