Abstract:The sesquiterpenes of the oleoresin essential oils of Dipterocarpus tubinatus Gaertn. f. and D. retusus Bl. were analyzed by GC and GC / MS / DS for relative contents and season-al variations. The main compounds in the oleoresin essential oil of D. tubinatus are δ-elemene, α-gurjunene, γ-murolene, α-cadinene, and the α-gurjunen relative content is highest. Then, the main compounds in oleoresin essential oil of D. retutsus are allo-aromadendrene and α-humulene, and the allo-aromadendrene relative content is highest. Seasonal variations were different at highly levels for δ-elemene. α-gurjunene, γ-muurolene, α-cadinene, β-cubebene, γ-elemene between the oleoresin essential oil collected in dry season and the oleoresin essential oil collected in rain season of D. tubinatus. But the composition of the oleoresin essential oil of D. tubinatus was not affected by season.