Brucea javanica (Simaroubaceae) is a medicinal plant traditionally used in Southern of China to treat several diseases. In order to enlarge the medication parts, the constituents of essential oils which extracted with microwave-assisted hydrodistillation (MAHD) and hydrodistillation (HD) from Brucea javanica were analyzed by capillary GC-MS and elucidated based on the standard mass spectral data. 42 and 37 kinds of volatile components were identified respectively. Relative mass fractions of the constituents were determined by area normalization method. The identified relative contents of essential oils were 94.09% and 94.13%, respectively. There were differences among some chemical constituents of two kinds of essential oils. But their main constituents were safrole, ( )-4-carene, ?-myrcene, eugenol methyl ether, 2,6-dimethoxy toluene, limonene and estragole.