Abstract: Trichoderma koningii, T. reesei and T. harzianum were tested for their ability to control Sclerotium rolfsii damping-off of tropical pine seedlings. Light microscopic observation on dual culture assay showed that the hyphae of all Trichoderma isolates could grow parallel to the hypae of S. rolfsii. However only T. reesei and T. harzianum coiled around the hyphae of S. rolfsii and formed appresoria and hook-like structures. Both isolates indicated equally high colony growth inhibition toward S. rolfsii. In greenhouse experiment, formulated T. reesei and T. harzianum in alginate beads, applied 4 days before S. rolfsii infestation controlled damping-off in pine seedlings effectively. Disease reduction by formulated all Trichoderma spp. decreased drastically when applied 4 days after or at the same time of S. rolfsii infestation.