In Argentina, the study of feeding habits of bats was practically restricted to frugivorous species, whereas data on the insectivorous bat diet was scarce and anecdotal. Thus, the aim of this study was to analyze the diet of Tadarida brasiliensis along the Yungas Forest, Argentina, at sites with different degrees of disturbance. Through the analysis of feces, arthropod orders were identified, volume and frequency of occurrence were estimated for each food item, and the niche breadth was estimated for the species. Finally, the diet was compared between capture sites, sexes, and seasons; finding variations among sites and seasons. The diet of T. brasiliensis contains arthropods belonging to nine orders and one undetermined taxon. Lepidoptera, Hymenoptera, and Coleoptera represent the highest volume proportions in the diet. The results add new and important information about the biology of T. brasiliensis in the southern part of its distribution.