This paper reports on part of the species of the marine isopod genus Serolis (Crustacea, Flabellifera, Serolidae) collected from benthic stations performed during one of the cruises of the Brazil ian Navy Oc/S "Almirante Saldanha" along southern South America. The species reported are Serolis polccris Richardson, 1911, Serolis elliptica Sheppard, 1933, Serolis uaperta Moreira, 1971, and Serolis foresti Bastida & Torti, 1970. A complete synonymy is given for each of these species, as well as the main distinctive characteristics enabling its ready recognition. Some remarks are provided on features not lengthned treated on previous accounts. The geographi cal distribution of all named taxa is given. Serolis uaperta is for the first time reported from off State of Rio Grande do Sul (Brazil) and Uruguay, extending considerably southernwards its southern limit of distribution. Both Serolis foresti and Serolis elliptica are also for the first time recorded from off Uruguay.