Resumo. The Montane Forest situated at the watersheds of Serra do Mar, state of Rio de Janeiro, presents environmental services that contribute for diverse segments of society, which demands water in quantity and with quality, as well as sustainable environments. Water vapor condensation at forest canopies is one of these services, as it contributes positively with hydrological water balance. It`s understanding can help the equation of solutions on sustainable environment planning, which motivated the study of horizontal interception (IH) on a Mountainous area in Nova Friburgo region. It was collected and analyzed data from total rainfall (PT), pluviometric rainfall (P), IH, internal precipitation (PI) e canopy interception (IC) during December 2003 to January 2004, at the windward slope of Serra do Mar, in Nova Friburgo. Values for total rainfall (PT) and horizontal interception (IH) corresponded to 786.23 mm and 68,71 mm, respectively. The lost from IC where of 25.46% and PT was 125.66% in relation to P, showing that IH influenced on the regional hydrological balance, constituting an important environmental service for ecosystem and population who depends on the watershed studied.