In this study, pellet compositions of Long-eared Owl (Asio otus) were analysed. The primary aim of this study was to investigate the diet composition of Long-eared Owl in high altitude steppe in summer. Compositions of 130 pellets of Long-eared Owl were used in the study. 147 preys (1.13 preys per pellet) which belong to 9 different taxa were found in pellet composition. A significant part of the diet in study area consisted of small mammals. Only two remains of birds were recorded from pellets. Microtus sp. was found important prey in the diet of Long-eared Owl (F = 81.63 %, B = 78.21%). Since Microtus sp. is the favourite prey of Long-eared Owl, this situation causes a negative correlation with the prey variety in diet composition. For this reason, FNB and Shannon-Wiener indices had low levels, Shannon-Wiener (H’) value was found to be low for Long-eared Owl.