Calomys is a rodent genus widely distributed in South America comprising 13 species, the most of species associated with savannas and grasslands in Brazil, Bolivia, Peru, Argentina, Paraguay, Uruguay, and Chile. Among Calomys species, two Brazilian endemic species have small distributions, C. cerqueirai and C. tocantinsi, this latter known only for seven localities. Here we extend the distribution of C. tocantinsi in 400km to the north, up to Canaã dos Carajás, in the Brazilian state of Pará. Our data suggest that this species is not endemic to the Cerrado and transition areas, but also occurs in the Amazon domain.