Rainfall interception losses were monitored for six months and related to vegetation and rainfall characteristics at the BPK-ODA research site in the upper stream of Mentaya river, Central Kalimantan. The rainfall interception losses were quantified based in the records of 52 selected rainfall events within the range of 8.5-135.5 mm. Over 6 months in one hectare pristine tropical rainforest, 217 mm (11%) of 1990 mm gross rainfall occurring in the research was loss to the atmosphere. Canopy through fall equaled 1745 mm (87.7%) of gross rainfall whereas stem flow represented 28 mm (1.3%). These findings are comparable to interception studies carried out in Sabah and Amazonian rainforest.