Abstract The presence of small mammals in the winter diet of a dormitory made up of 5 specimens living at the WWF's Oasi San Giuliano (province of Matera) is analysed in the following study. The data confirm the presence of small mammals, Microtinae in particular, as a main prey of the Long-eared Owl. 1921 prey-individuals totalling 37695 grams in biomass were found. Rodentia are dominant (86.93% of the biomass); Microtus savii is of particular importance and represents 61.06% of the total biomass and was found in 60.42% of the pellets found. The second most frequently hunted species is the Apodemus sp.: 24.06% of the biomass, 37.08% of the frequency. The other mammals preyed on (Suncus etruscus, Crocidura sp., Pipistrellus sp., Vespertilius sp., Rattus sp., Moscardinus avellanarius) are of little importance: 1.27% of the biomass. The owls preyed upon 9 of the 11 species of mammals present (the Talpa sp. and the Mus domesticus are absent). Affinity among different periods, estimated through Sorensen's Index, was found to be medium-high (0.67-0.72). The data analysis confirms the stenophagy of the Long-eared Owl, in this area that is characterised by extensive cereal cultivation and few shrubs and trees. In comparison with other Italian localities, a greater number of preyed species was recorded (8 mammals, 9 birds, 1 insect). Roost owls preyed mainly upon Chiroptera (0.36% compared with 0.1-0.2). Myotis capaccinii and Pipistrellus savii were also found in the diet of the Long-eared Owl for the first time in Italy.