The diet of Arctocephalus australis was studied through fecal analysis, from September of 1995 to May of 1998, in Isla de Lobos (35°01′50″S-54°53′00″W), Uruguay. A total of 539 scats analyzed indicated that the weakfish (Cynoscion guatucupa), the cutlasfish (Trichiurus lepturus), the anchoveta (Engraulis anchoita), the anchovy (Anchoa marinii), and cephalopods were the main prey consumed by these fur seals. Prey richness was higher during January. The diet of A. australis varied between years, apparently related to changes in prey availability. C. guatucupa and E. anchoita decreased while T. lepturus and cephalopods increased from 1996 to 1998. South American fur seals fed on fish ranging in length from 5.4 to 104.8 cm and from 0.7 to 629.9 g in wet mass. However, the mean mass of the main items was never more than 200 g. Observations suggests that A. australis is a trophic generalist with the potential to prey on a wide range of species, although most of the diet is comprised of relatively few species. Fur seals and artisan fisheries both took C. guatucupa, with fur seals taking younger individuals (1–2 yr) than artisan fisheries (> 3 yr).