The meridional serotine Eptesicus isabellinus (Temminck, 1840) has recently been identified as a cryptic species that occurs in the south of the Iberian Peninsula. Little is known about its ecology. We used morphological analysis of droppings from an urban semiarid Mediterranean landscape to determine seasonal differences in diet. We identified 15 insect prey types and found significant seasonal differences in the consumption of seven prey types. The diet of E. isabellinus was dominated by Scarabaeidae (Coleoptera) and Diptera, and there were seasonal changes in the consumption of Carabidae (Coleoptera), Lepidoptera and Cercopidae (Hemiptera). Shannon-Wiener and Levins' indices showed that the diet was more diverse during the post-hibernation and pregnancy periods. Pianka's index showed that there was relatively low dietary overlap between periods. The seasonal changes recorded between different physiological periods could be related to changes in the energetic needs of the individual or to variation in preyavailability. Although E. isabellinus mainly eats Scarabaeidae and Diptera, it can show flexibility for example by hunting insects that fly around blossoms such as chafers Melolontha spp.