Here we describe a new species of the Ischnocnema parva species series from the Parque Estadual do Desengano, in the northern part of the State of Rio de Janeiro, Brazil. We use morphology and mtDNA sequences to allocate the new species into the I. parva species series. The new species is closely related to I. parva genetically and morphologically, from which it is diagnosable by (1) the presence of a well-developed calcar tubercle, (2) a reduced Toe I, (3) a deep V-shaped median slit on the dorsal surface of toe discs, and (4) externally indistinct tympanum and tympanic annulus.