Most bears are opportunistic omnivores; their diets consist of fruits, other vegetative material, and in lesser amounts, mammals, fishes, and insects. Sloth bears (Melursus ursinas) are the only species of ursid specifically adapted to feed on insects, especially termites and ants, although they also feed on fruits when available. We studied diets of sloth bears in Royal Chitwan National Park, Nepal, where fruits are available for ca. 4 months (May–August) and access to colonies of termites is reduced in lowlands that are flooded during the fruiting season. We analyzed feces and observed sloth bears foraging to investigate their responses to changes in availability of food. Diets of sloth bears were dominated by insects (>90%), especially termites (≥50%), from September through April, but they relied heavily on fruits from May through August. Seasonal movements between lowland and upland habitats seemed to be prompted mainly by availability of termites. Termites were more dominant in the diets of sloth bears in our study than in a study conducted 20 years ago in Royal Chitwan National Park and in studies in India. The dietary shift of sloth bears in Royal Chitwan National Park may have been related to changes in habitat conditions associated with relocation of people out of the Park. It appears that sloth bears, like other bears but unlike other myrmecophagous mammals, can adapt their diet to changing food conditions.