The rock frog (Thoropa taophora) dwells from rocky seashores to rocky outcrops within the Atlantic rainforest on coastal areas of the state of São Paulo, southeastern Brazil. In this study, we provide data on the food habits of a rock frog population focusing on ontogenetic, sexual, and seasonal variation. The study was based on the examination of 356 individuals (154 adults, 82 juveniles and 120 froglets). A total of 26 invertebrate types were found in the diet of T. taophora. The commonest prey types in the three size classes (adults, juveniles and froglets) of rock frogs were ants, both in frequency and number. Prey composition differed significantly among size classes, except for beetles and spiders. Prey composition of males and females also differed significantly: females had a high proportion of marine isopods, caddisfly nymphs, and orthopterans in the diet, whereas males had a high proportion of ants and caterpillars. Seasonal changes in diet (all significant) in the three size classes include froglets eating more springtails and less mites in the dry season, juveniles eating more marine isopods during the wet season (similar difference for adult males), and adult females eating more ants during the wet season.