The feeding ecology of the White-tailed Hawk (Buteo albicaudatus albicaudatus) was studied in south-eastern Brazil. The aims of this study were to: (1) quantify the diet of the White-tailed Hawk, including the number of prey species eaten and their biomass; (2) investigate the influence of season on diet; and (3) describe the breadth of the diet. Pellets found beneath seven White-tailed Hawk nests and several roosting sites around the nesting sites were collected from September 2000 to September 2001. The analysis of 259 pellets revealed 31 prey species or morphospecies, 3296 individuals and 7.2 kg of estimated consumed biomass. Five insect orders (Hymenoptera, Heteroptera, Odonata, Isoptera and Lepidoptera) and one vertebrate order (Chiroptera) were reported as prey for the first time for this species. By number, invertebrates made up 88% of all prey items, 63% of which belonged to a single orthopteran family (Acrididae). Among vertebrates, rodents were the group most consumed by number and represented 73% of all vertebrate prey items. However, in terms of estimated biomass consumed, the most represented groups were rodents (50%), orthopterans (21%), birds (11%) and lizards (7%). Vertebrates alone yielded 77% of the total biomass consumed. Whereas the White-tailed Hawk may be classified as insectivorous by number of prey, it is carnivorous with respect to biomass ingestion. According to the Levin’s diet-breadth index, this raptor could be considered to be a specialist predator of grasshoppers (Acrididae) by prey number and of rodents by prey biomass. Food eaten was dependent on season, with more mammals taken during the dry (breeding) season and a broader range of prey during the wet season.