The knowledge of the diet of endangered species provides information on ecology and behaviour that is essential for the adequate management of their populations. Population decline may be indeed associated with diet specialization and unavailability of feeding resources, especially in modified environments. We studied the diet and prey selection of Rhinolophus hipposideros Borkhausen, 1797 in a modified Mediterranean landscape in Portugal, where this species is classified as vulnerable. Diet composition was evaluated by analyzing faecal pellets collected in a breeding colony of R. hipposideros, and the available arthropods were sampled using a light trap set outside the roost. The most consumed prey were Lepidoptera, Tipulidae (Diptera), Hymenoptera, Diptera and Neuroptera. Arthropod diversity remained fairly constant in the diet, but not in terms of prey availability. Our results show that R. hipposideros is a generalist species that feeds on a great number of prey species. However, our data suggest that, within the broad dietary niche, R. hipposideros is not opportunistic, actively selecting Diptera as a preferred food item. Despite the marked differences in foraging habitats, our results are closely match to those of studies done in Western and Central Europe, suggesting that R. hipposideros feeds on similar taxa all across Europe. However, as many studies indicate, this species selects broadleaved woodlands and riparian vegetation to forage, so conservation measures should take into account the protection of native forest and the maintenance of forest corridors among them, as R. hipposideros seems to avoid crossing open areas.