The fishing bat, Noctilio leporinus, is common throughout the West Indies, where it feeds on fish and insects. Anecdotal observations in Cuba suggest that this bat could prey on other species of bats, at least when they are kept together in captivity. We examined the diet of this species at three caves in the northwestern part of Puerto Rico, namely Amador Cave in the Municipality of Camuy, and Ventana and Matos Caves in the Municipality of Arecibo. Four guano traps were set under the roosting sites of N. leporinus once a month. Traps were left overnight and recovered fecal remains were examined in the laboratory under a dissecting microscope. Our results indicate that, in addition to insects and fish, N. leporinus in northwestern Puerto Rico is preying on other species of bats. Three species of bats were recovered under the roosts of N. leporinus. It appears that this behavior is more common during the breeding season of fruit-eating bats, when N. leporinus seem to prey opportunistically on the young of Brachyphylla cavernarum.