The Austral Peregrine Falcon (Falco peregrinus cassini) is widely distributed in Argentina, although studies on its diet are limited. Here we report information on the diet of this falcon in southern Atlantic Patagonia, Argentina. During November and December in 2009 and 2010, we visited nest sites of Austral Peregrine Falcons to collect prey remains to investigate their diet during the breeding season. We identified 72 avian prey remains from seven eyries in 2009 and three eyries in 2010. We documented seven orders of nonpasserines (11 families representing at least 58 individuals [81% of total prey items]). For the order Passeriformes, seven families were represented by 14 individual birds (19% of total prey items). In all, we identified 52 prey remains (72% of total prey items) to the species level. Another 12 birds were identified only to genus and three only to family or subfamily. Body mass for avian prey identified to species (n = 51) ranged from 10.4 g (Troglodytes aedon) to 842 g (Mareca sibilatrix). Nonpasserines provided 96.2% of the estimated biomass of the prey. Although our sample size is limited, compared with previous reports conducted more than 30 yr ago or in recent years but limited to one pair, our observations for ten nests in 2 yr provide novel and current information on avian prey species of Austral Peregrine Falcons. Our study increased the number of prey species documented for these birds for a geographical region where diet information was almost nonexistent, and provided diet data for both the typical and pallid color morphs of this subspecies.