il suffit d'ajouter ce code dans template.php :

/**
* Add unique class (mlid) to all menu items.
*/
function YOURTHEMENAME_menu_link(array $variables) {
$element = $variables['element'];
$sub_menu = ''; $element['#attributes']['class'][] = 'menu-' . $element['#original_link']['mlid'];

if (

$element['#below']) {
$sub_menu = drupal_render($element['#below']);
}
$output = l($element['#title'], $element['#href'], $element['#localized_options']);
return '<li' . drupal_attributes($element['#attributes']) . '>' . $output . $sub_menu . "</li>\n";
}