The root of Astragalus membranaceus Bunge (Leguminosae), which has been used for the treatment of hypertension, chronic hepatitis, duodenal ulcers, chronic nephritis and promotion of immunity in folk remedies. Several lines of evidence indicate that oxidative modification of low-density lipoprotein (Ox-LDL) may play an important role in atherogenesis. Hence, the role of antioxidants in the prevention of LDL oxidation needs to be determined. To investigate the antioxidant activity. we determined the MeOH ex. and fractions of Astragali Radix on the inhibition of LDL oxidation. The CH$_2$C1$_2$ and EtOAc orations inhibited the oxidative modification of LDL by a decrease in the lipid peroxide content and the electrophoretic mobility of LDL. Calycosin-7-0-$eta$-D -glucoside which was isolated from EtOAc fraction inhibits the oxidative modification of LDL.