We observed an active nest of the Grey-bellied Hawk (Accipiter poliogaster) in the mixed rainforest of southern Brazil during the 2011 breeding season. The nest was a platform built in the branches of the upper part of a Paraná pine (Araucaria angustifolia). The clutch size was two eggs, but only a single nestling survived and left the nest, ∼49 days post-hatching. The fledgling was fed by adults at the nest for at least 90 days post-hatching. Only the adult female incubated the eggs and brooded the nestlings. Both female and male provided nest defense, the former up to 50 m from the nest and the latter at 50 to 200 m. Only the male hunted and only the female fed the nestlings. The identified prey brought to the nest by the male included eight birds and one young armadillo. Five voice types were identified: one alarm call, three food-related calls (performed by adults), and one food-begging call (performed by the fledgling). The type of habitat where the nest occurred suggested this poorly known species can possibly survive in disturbed areas. It seems to be naturally rare and its' shy behavior contributes to its low detection.