The semiaquatic snake Erythrolamprus miliaris has a wide distribution in cis-Andean South America and is often locally abundant. Nevertheless, there is still comparatively limited information available on its ecology. In the present study, we analyzed the diet of E. miliaris in five different regions along the Atlantic Forest domain in eastern Brazil, based on the stomach contents of specimens deposited in scientific collections. Overall, only 10.2% of the stomachs contained identifiable food items, the most frequent of which were fishes and postmetamorphic anuran amphibians (present in 41.8% and 53.7% of adult stomachs, and 17.9% and 75.0% of juvenile stomachs, respectively). Diet composition was fairly similar among populations, indicating a low geographic variability in the species feeding habits. Our data suggest that younger snakes feed mainly on anurans, tending to consume more fishes as they grow larger. Consumption of toads of the genus Rhinella indicate that E. miliaris is resistant to bufonid toxins, as are other members of the tribe Xenodontini.