A new bufonid toad is described. The species belongs to the genus Melanophryniscus, and may be the largest species in this genus. Its size and external features (pale green in dorsal surface) resemble those of Melanophryniscus cambaraensis and Melanophryniscus macrogranulosus, from which it differs by the absence of frontal swelling. At present, the new species is endemic to the southern border of the Brazilian Southern Plateau, in central Rio Grande do Sul state.