Introduced predators have had, and continue to have, severe impacts on Australian biodiversity. At a recently established conservation reserve, Witchelina, in arid South Australia, we assessed the diet of feral cats (Felis catus) (404 samples), red fox (Vulpes vulpes) (51 samples) and dog (Canis familiaris) (11 samples) over a 3-year period. There was marked overlap (98.5%) in dietary composition between cats and foxes. Rabbits (Oryctolagus cuniculus) comprised a major dietary item for all three predators. Invertebrates contributed the largest number of prey items for foxes and cats, but mammals comprised the bulk, by weight, for all three predators. Birds and reptiles had a higher frequency of occurrence in the diet of cats than of foxes or dogs. The size of mammal prey taken was least for cats and greatest for dogs. The diets of cats and foxes showed significant seasonal variation, with reptiles and invertebrates being least common in the diet in winter. The threatened thick-billed grasswren (Amytornis modestus) was found for the first time in the diet of feral cats. Bearded dragons (Pogona vitticeps) occurred in about one-third of cat and fox samples. This study contributes further to the evidence of biodiversity impacts of introduced predators, and the need for their strategic management.