This paper provides the description of a new species in the genus Zabius Thorell (Scorpiones, Buthidae), Z. gaucho n. sp., from four localities in the State of Rio Grande do Sul, Brazil. It differs from Zabius fuscus (Thorell 1877) and Z. birabeni Mello-Leitão 1938 in details of the telson shape, the longitudinal carinae on mesosomal tergites II-VI, and the number of pectinal teeth. The genus was hitherto known only from Argentina, Z. fuscus being a frequent inhabitant of the central Sierras; Z. birabeni, in turn, is probably a rare and non-orophilous scorpion, collected in scattered localities on the monte/chaco ecotone and in northern Patagonia. The presence of a species of Zabius in southern Brazil lends additional support to the generalized distributional track known as “peripampasic track,” which zoogeographically links the central Sierras Pampeanas with ancient mountains in the southern province of Buenos Aires, southeastern Uruguay and southern Brazil.