In tropical forests, large frugivores are assumed to be important seed dispersers for many large-seeded trees such as Aglaia (Meliaceae), a widespread and common genus. We investigated the seed dispersal of Aglaia spectabilis, a large-seeded tree species in a moist evergreen forest of Khao Yai National Park in Thailand. In quantitative aspects of seed dispesal, we assessed both the frugivore assemblages foraging on arillate seeds of Aglaia spectabilis and dispersing them and the seed predator assemblages, thereby covering dispersal as well as the post-dispersal aspects such as seed predation. The results showed that frugivores dispersing seeds were a rather limited set of four hornbill and one imperial pigeon species, whereas two squirrel species were not dispersers, but dropped the seeds on the ground. In qualitative aspects of seed dispersal, we combined data from feeding trials, germination tests, and radio-telemetry of hornbills and estimated the seed dispersal distance. We also marked all the individuals of Aglaia spectabilis within 4-ha and followed their survivorships for a period of 15 years. Hornbill gut passage had a positive effect on the germination rate of Aglaia spectabilis and were capable of dispersing seeds over several kilometers. Some seedlings of Aglaia spectabilis were distributed far from the fruiting trees and survival of 1-yr seedlings after 15 years was relatively high (16%). Heavy seed predation by mammals around fruiting trees together with high seed removal rates, short visiting times, relatively long seed dispersal distance, and regurgitation of intact seeds by mainly hornbills lead us to the conclusion that hornbills show high effectiveness in dispersal of this large-seeded tree species.