The diet of Tawny Owl Strix aluco was studied in the area of Slovenske gorice - NE Slovenia. The analysis was carried out by examining pellets collected at ten locations in the period from 1984 to 2015. From the pellets, 2,121 prey units were isolated. The predominant prey were mammals (Mammalia, 84.8%), followed by birds (Aves, 8.3%), insects (Insecta, 4.7%), frogs (Anura, 1.6%) and earthworms (Oligochaeta, 0.5%). Four orders of mammals were found: rodents (Rodentia), insectivores (Insectivora), bats (Chiroptera) and carnivores (Carnivora). The most frequent prey in the owls’ diet were voles (Arvicolinae, 46.6%) and mice (Murinae, 28.8%), while the number of shrews (Soricidae) was low (4.5%). The obtained results are in concordance with the conclusions of other studies. In the area of Slovenske gorice, the Tawny Owl is an opportunistic predator of small mammals with an emphasis on voles and mice. Prey frequencies differ significantly among some localities. Variability in proportions of prey species among localities can also be the result of sampling carried out in different seasons and variability in the population dynamics of small mammals among years. Challenges for future research are to describe seasonal variability of the diet and to evaluate interspecific competition within the guild of night predators of small mammals: Tawny Owl, Long-eared Owl Asio otus, and Barn Owl Tyto alba, which are sympatric in this area.