Hexane, Hexane/diethylether and chloroform fractions from Panax ginseng C.A. Meyer stroungly inhibitied human platelet aggregation induced by a high dose of thrombin (2$mu$/ml). Chloroform fraction more strongly inhibited the platelet aggregation than the other two fraction among them. There were fatty acid ester and phosphate ester instead of polyacethylene compounds in the chloroform fraction.