We analyzed the diet of a litter-dwelling microhylid frog, Chaperina fusca, from the lowland rainforest of Borneo. We flushed the stomachs of 194 frogs: 94.8% had contents and 5.2% were empty. Although the diet composition of C. fusca was diverse, with 27 prey categories, we found that ants, mites, beetles, and springtails, in that order, dominated its diet both numerically and volumetrically. Among these four categories, however, ants were by far the most frequently consumed in both number (63.5%) and volume (82.6%) and in higher proportion than in the leaf litter. A novel aspect of our study, conducted in only a limited number of studies of anuran diets, was to determine the ant genera consumed. We identified 41 ant genera consumed by C. fusca whereby the genera Lophomyrmex, Pheidole, and Tetramorium were the most prominent. We also recorded a significant relationship of prey volume and number with both body size and mouth width of frogs. Our data provide circumstantial evidence that C. fusca is an ant-specialist feeder and active forager. These results are in line with the dietary characteristics of many terrestrial microhylid frogs in subtropical and tropical Asia, the Neotropics, and the Afrotropics.