Two new Nemesiidae species from Reserva Biológica do Tinguá, Rio de Janeiro, Brazil are described. Acanthogonatus minimussp. nov. differs from the remaining species of the genus by the male palpal bulb, which has very long and twisted embolus, ca. 2/3 the length of the palpal tibia, long and twisted spermathecae, anterior eye row recurved and fovea T-shaped. Chaco tinguasp. nov. differs from the remaining species of the genus by the retrolateral megaspine on tibia I, palpal embolus tip hook-shaped, inferior tarsal claw on all legs, absence of pubescence on the carapace and legs. Both species were collected with Winkler extractors in leaf litter. They are the smallest specimens in their respective genera and also among the world Nemesiidae described to date. The smallest male of A. minimussp. nov. measures 4.22 mm and of C. tinguasp. nov. measures 3.85 mm. Data on the phenology of C. tinguasp. nov. is presented.