Nyctinomops macrotis, the big free-tailed bat, is relatively uncommon in the southwestern United States, and diet information for this species is sparse. The objective of this study was to examine the diet of N. macrotis in Big Bend National Park, Texas, by using fecal analysis to determine what these bats ate in an area where they were sympatric with 3 other species of free-tailed bats. We collected and analyzed fecal samples from 40 individuals and obtained the following results: Lepidoptera (87.5% volume, 100% frequency), Hemiptera (4.1% volume, 22.5% frequency), Coleoptera (4.6% volume, 17.5% frequency), Orthoptera (1.1% volume, 12.5% frequency), unidentified insects (2.4% volume, 30.0% frequency). The diet of N. macrotis largely overlapped that of the Mexican free-tailed bat (Tadarida brasiliensis) and pocketed free-tailed bat (Nyctinomops femorosaccus) in Big Bend National Park. However, N. macrotis consumed significantly more lepidopterans and significantly less hemipterans and coleopterans when compared to these other 2 molossid species. In addition, proportions of insects taken differed among the 3 bat species in some months.