Croplands have expanded dramatically during the last century, frequently leading to severe biodiversity losses within occupied areas. In addition to such direct influences, croplands may also have affected biodiversity within adjacent natural habitats, yet such potential indirect effects have rarely been quantified. Here, we test for effects of cornfields on small mammal communities inhabiting forest fragments in the Atlantic Forest biodiversity hotspot, Brazil. We test the hypotheses that cornfields increase the abundance and dominance of granivorous small mammals in adjacent forest fragments but reduce the abundance of nongranivorous species and community richness. To test these hypotheses, we used a replicated randomized block design, comparing communities located at forest interiors, forest-cornfield edges, and also forest-road edges. The abundance of granivorous small mammals was significantly higher at forest-cornfield edges compared to the other treatments, whereas insectivorous—omnivorous species had an apparently neutral response to the edges. Forest-cornfield edges harbored fewer small mammal species and tended to have a greater dominance of granivores. Forestcornfield and forest-road edges harbored species characteristic of both forested and nonforested habitats. Our findings suggest that cornfields alter the structure of native small mammal communities, mostly by providing complementary resources for granivores.