A new species of Adiantum, A. pulcherrimum Prado, is described from the Atlantic forests of Rio de Janeiro and São Paulo States, and inland forest from Minas Gerais State, Brazil. It can be distinguished by long-creeping rhizomes, stipes with scattered minute and light brown hairs, laminae glaucous abaxially, median segments curved basiscopically, segment apices mostly long-acuminate or acute, and glabrous indusia. Illustrations of the diagnostic characters of the taxon as well as a key for the related species in Brazil are also presented.