Ecotourism has great potential to benefit protected areas. In addition to the economic impact on local communities, it has generated increased political and financial support for conservation. However, tourist activities can negatively impact natural environments. In this study we evaluated the impact of rafting activities on medium to large terrestrial mammals in the Serra do Mar State Park/Santa Virgínia Unit (PESM/NSV). We installed camera-traps along the Paraibuna river in areas with and without rafting and hiking activities. We found that both species richness and abundance of medium to large terrestrial mammals were negatively affected by rafting, but not by hiking. The white-lipped peccary (Tayassu pecari) was the species most affected. However, this impact should be monitored in the medium to long term, given the lack of data previous to the implementation of these activities and the possible habituation of the species over time. In such context, future studies should test variable frequencies of rafting activities to estimate its cost-benefit relationship with conservation units of Atlantic Forest.