This paper reports the description of immature stages (larva, protonymph and deutonymph) as well as redescription of the adults, female and male, of Kuzinellus kuzini (Wainstein, 1962), collected from a walnut infested by the leaf gall mite, Aceria tristriatus (Nalepa), in the Hamedan and Lorestan Provinces, Iran. Furthermore, a key and table to the characteristics of all mobile stages are provided