Rousettus obliviosus is a megachiropteran bat endemic to the Comoros Islands in the western Indian Ocean. The species is broadly distributed on Grande Comore, Mohéli, and Anjouan, but appears to be absent from Mayotte. Roost sites were found to be both shallow and deep caves, in dark locations with infrequent human disturbance. Colony size ranged from 100 to several thousand and at two sites seasonal variation was observed. Total estimated population size was 7,100–17,100. R. obliviosus fed on a variety of native and non-native tree fruits and flowers, and was found in native forest habitats, underplanted forest and agricultural areas. R. obliviosus is a manoeuvrable flyer able to hover for brief periods and may echolocate. A small range, sensitivity to disturbance, limited roost site availability and deforestation combine to threaten this species. We suggest that the current IUCN Red List status of Lower Risk: near threatened should be revised to Vulnerable. Protection of roost sites, further surveys to identify additional roosts, further ecological research, and protection of remaining forest are conservation priorities for R. obliviosus.