Six triterpenoids, chiisanogenin, chiisanoside, ursolic acid, oleanolic acid, beta-sitosterol and daucosterol, were isolated as the platelet anti-aggregating components from the leaves of Acanthopanax senticosus and the fruits of A. sessiliflorus. Chiisanogenin showed about 50-fold higher potency than acetylsalicylic acid (ASA) on U46619-induced platelet aggregation (IC50: 6.21 muM) and 10-20-fold higher effects than ASA on epinephrine- and arachidonic acid (AA)-induced aggregation (IC50: 2.50 and 4.81 muM, respectively).