The present study characterized the diet of Aegla longirostri from southern Brazil, in relation to seasonality, size and sex of the animals. The aeglids were sampled bimonthly, from October 1999 to August 2000. The animals were dissected and the Stomach Repletion Degree (RD) and the food items contained in each stomach were recorded. For each food item with RD⩾0.5, the Relative Importance Index (RII) was calculated. Of 399 animals collected, 305 had RD⩾0.5. The following items were found in the stomachs: plant tissue, non‐identified material, sediment, and fragments of adult insects, as well as fragments of Aegla sp., mollusc shells, fish scales and dipteran larvae. Independently of size class and sex, the animals showed a preference for plant tissue. These results demonstrate that A. longirostri has an omnivorous feeding habit, and is mainly herbivorous.