Ganoderma sp. is a pathogenic fungus that can cause root rot in sengon (Falcataria mollucana) plantation. Ganoderma sp. is difficult to detect because the symptoms are simillar to symptoms of other root diseases. The experiment was conducted at the Laboratory of the Faculty of Forestry IPB with aims to determine in vitro growth rate of colony diameter of Ganoderma sp. and Trichoderma spp. and also to obtain the ability of Trichoderma spp. in inhibiting the growth of colonies of isolates of Ganoderma sp. on PDA and MEA medium. The result shows that diameter of colony isolat Ganoderma sp. growth on PDA media (7,09 mm/day) was faster than the growth on MEA media (5,41 mm/day). The growth rate of the colony diameter of Trichoderma spp. isolates on PDA were 69,67 mm/day, 56.49 mm/day, and 42,04 mm/dayfor T.viride, T.harzianum and T.pseudokoningii, respectively. While, using the MEA media obtained an average value of growth of diameter colony isolates were 77,29 mm/day, 66,50 mm/day, and 59,67 mm/day) for T.pseudokoningii, T.harzianum and T.viride, respectively. The highest percentage of inhibiting barriers of Trichoderma spp. was T.harzianum than T.pseudokoningii (59,76%) and T.viride (46,47%).