A new species of Pheraeus Godman, 1900, P. guandu Saraiva, Carneiro, Mielke & Casagrande sp. nov., restricted to the Rio Doce Valley (Espírito Santo and Minas Gerais, southeast Brazil) is described. Adults of the new species are illustrated and compared with phenotypically closest species, Pheraeus argynnis (Plötz, 1884), together with the diagnostic characters present in the male and female genitalia. This new species is here solely described because it is known to occur in a restricted region crossed by the Rio Doce. This region has been extensively transformed in recent decades by agriculture, livestock, construction of hydroelectric and tailing dams, and more recently by a dam failure, thus potentially impacting the habitat of this species.