Because of the worldwide distribution of the Barn Owl (Tyto alba) and the easily way to find its pellets, it is often used to diet studies. To investigate the eco-geographical impact of mountainous areas on its diet, we conducted studies in the Jura, Alpes, Central and Pyrénées mountains and we also did pellet analysis from 8 sites in the Jura mountains. Analysis of the tooth and skull content of pellets allowed us to draw up two types of change in the diet of Tyto alba in correlation with mountain elevation. The first one concerns the Jura, Alpes and Central mountains, where the diversity of the diet declines with the increase in elevation. The second one concerns the Pyrénées mountains, where there is no change in the diversity of the diet, perhaps because of the higher diversity of small mammals caused by mediterranean influence. Thus, it seems that elevation cau ses a decrease in diet diversity of Tyto alba in continental mountains (Jura, Alpes and Central mountains) probably because of more homogeneous landscapes dedicated to grass production. However, in Mediterranean mountains (Pyrénées), a more diversified small mammal guild provides a constant level of diet diversity.