The increase of alien invasive plants in biological reserves is a major threat to biodiversity in tropical areas. We surveyed invasive angiosperms in two national parks in West Java and estimated their potential effects on declining biodiversity. In 2010 and 2011, we surveyed three trails in Mt. Halimun-Salak National Park (HSNP) and three trails in Mt. Gede-Pangrango National Park (GPNP). At 50-m intervals along trails from the park border to the interior, we recorded species name and coverage of invasive plants, trail width, and degree of vegetation cover of all species. Excluding members of Poaceae and Cyperaceae, 31 invasive species were found: 19 along 13.75km of trails in HSNP and 29 along 11.45km of trails in GPNP. The number of species per 500m was 10.7 in HSNP and 8.6 in GPNP. All trails in HSNP and the nearest trail in GPNP had similar species compositions. Invasive plants along these trails may have the same origin: Bogor and Jakarta. The other two trails in GPNP seemed to be affected independently by invasion from Cibodas Botanic Garden and orchards, respectively. The number of invasive species along trails was most significantly correlated with elevation, followed by distance from the park border, and trail width. The significant relationship with distance from the border highlights that a nature reserve with the same area but a longer border has a higher risk of invasion than one with a shorter border.