The Atlantic Forest is one of the most biodiverse biomes in the world and has been severely degraded and fragmented, with the extirpation of most medium-sized and large vertebrates from the forest remnants. Here we present the results of a survey of medium-sized and large mammals in an area of protected seasonal semideciduous forest, the Floresta da Cicuta Area of Relevant Ecological Interest (ARIE-FC), Rio de Janeiro, Brazil, part the Atlantic Forest biome. We used camera traps (2,257 camera days) and direct observations over a 23-month period. We recorded 19 species (including two domestic species), seven of which are classified as at-risk, such as Leopardus guttulus (Hensel, 1872), Sylvilagus tapetillus Thomas, 1913, Alouatta clamitans Cabrera, 1940, and Chrysocyon brachyurus (Illiger, 1815). A diverse terrestrial mammal assemblage in the ARIE-FC reinforces the importance of small forest fragments for the conservation of biodiversity in human-modified landscapes of the Brazilian Atlantic Forest.