All available specimens of Andescynodon mendozensis and Rusconiodon mignonei are examined and restudied, and the latter species is regarded as a junior synonym of the former. The postcranial skeleton of this species is described for the first time; it generally shows primitive features of traversodontids. Andescynodon mendozensis is a small- to medium-sized traversodontid characterized by 9∼11 upper postcanines in adults (fewer in larger individuals), the transverse ridge of upper postcanines lying anteriorly on the tooth, paracanine fossa penetrating the skull roof in adult; it is differentiated from Pascualgnathus by relatively flatten skull, shorter and narrower temporal region, presence of four rather than three upper incisors.