The red brocket (Mazama americana) and gray brocket deer (Mazama gouazoubira) are sympatric in the Atlantic Forest and present a number of ecological similarities in their diet and habitat use, although interspecific competition in these species is poorly understood. This study aimed to compare abundance and produce evidence of niche partitioning between these species. We estimated population density, activity patterns, habitat occupancy, and detection probabilities for the 2 species in a large remnant of the Atlantic Forest of Espírito Santo, Brazil. Abundance was estimated using the distance sampling technique, and occupancy, detectability, and activity patterns were assessed using camera-trap monitoring at 39 sample sites over a 1-year period. During surveys, we obtained 44 sightings of M. americana and 74 of M. gouazoubira, with 199 records in which the species was not discriminated. We applied a correction for the unidentified sightings to avoid underestimating density. The corrected population size estimates were 3,668 individuals (confidence interval [CI] 95%: 2,989–4,601) for M. americana and 6,701 (CI 95%: 5,857–7,667) for M. gouazoubira. Occupancy probability for M. americana was best described by the large trees density (diameter at breast height > 50 cm) and the edge forest distance, while M. gouazoubira did not present any habitat preferences based on the covariates used for modeling. M. americana was mostly nocturnal, whereas M. gouazoubira was active mainly during the day. We conclude that, despite the abundance of these sympatric species, and their occupation of the same habitats, they may avoid competing for habitat and feeding resources through differences in their activity patterns.