Sesquiterpenes of Korean ginseng (Panax ginseng C.A. Meyer, KG) and American ginseng (Panax quinquefolium, AG) were Isolated by simultaneous distillation and extraction (SDE) with 30% methanol and n-hexane or adsorption using C18 Sep-Pak . The sesquiterpenes in KG and AG were compared each other by using TLC and GC/MS. Thin layer chromatogram of KG gave 4~5 spots of terpenes colored by vanillin-sulfuric acid, while AG did one major spot. Total ion chromatogram of KG showed about 30 peaks of sesquiterpene having molecular weight 204. Among these, 9 components such as alloaromadendrene, germacrene B, isocaryophyllene, $alpha$-neoclovene, ${gamma}$-muurolene and $eta$-panasinsene together occupied 81.5% of total sesquiterpenes identified. In AG, however, only 3 components, i.e., isocaryophyllene, $eta$-bisabolene, $eta$-sesquiphellandrene occupied 79.3% of total sesquiterpenes identified. Especially isocaryophyllene was a dominant component of AG occupying 56.6%. Eight sesquiterpenes, including alloaromadendrene, germacrene B and $alpha$-humulene, were not detected in AG. These results indicate that sesquiterpenes could be used as indices for the chemical difference between KG and AG.