The essential oil from the root of Ostericum grosseserratum  (Maxim. ) Kitag. , a traditional Chinese medicine in China, was first isolated by GC method. 96 components have been identified by GC/MS. The main constituents are octanal, β-pinene, 4-methyl-1- (1-methylethyl )-bicyclo (3.1 ,0] hexan-3-ol, octahydro- 1.9.9-trimethyl-4-methylene- 1H- 7- methanoazulene, pcymene. a- pinene, heptanal, 3, 7-dimethyl- 1-octene, 2-decenal etc. The chemical data will provide basic information for the study of phytotaxonomy and economic utilization.