The root of Astragalus membranaceus (Leguminosae) has been used in traditional chinese prescriptions for strengthning the superficial resistance, promoting pus discharge and tissue regeneration, diuretis and alleviating edema. Lipid peroxidation has been suggested as a major cause of atherosclerosis, cancer, liver disease, and the aging process. In order to investigate the anti-lipid peroxidation activity, Astragali Radix was extracted with 80% MeOH and fractionated with hexane, CH2Cl2, EtOAc, BuOH and Water. The antilipid peroxidation activities of them were determined by human erythrocyte ghost and CCl4-induced lipid peroxidation. CH2Cl2 and EtOAc fractions, especially, isoflavonoids, 7,2'-dihydroxy-3',4'-dimethoxyisoflavan-7-O-β-D-glucoside and calyco sin-7-O-β-D-glucoside from EtOAc fraction showed anti-lipid peroxidation activities.