To examine the characteristics of antioxidative compounds from Capsella bursa-pastoris, ethanol extracts were separated into five organic solvent fractions; hexane(Fr.H), diethyl ether (Fr.E), ethyl acetate(Fr.EA), butanol (Fr.B), and water(Fr.D) fractions. Fr.B showed the greatest electron donating ability and inhibitory effect on lipid peroxidation. Whereas Fr.E had the most excellent activity in the superoxide radical scavenging activity by xanthine/xanthine oxidase-cytochrome c reduction system. The inhibitory effect of each fraction on xanthine oxidase was also measured. Fr.E had the strongest inhibitory effect on xanthine oxidase and IC_(50) was 5.65 ㎍. The results indicate that the superoxide radical scavenging activity of Fr.E is caused by the inhibitory effect on radical generating system of xanthine oxidase. Also the order of inhibitory effect on xanthine oxidase was Fr.B$lt;Fr.EA$lt;Fr.E. But Fr.D had not an effect on xanthine oxidase. The inhibition type of Fr.E on xanthine oxidase turned out to be a noncompetetive inhibition. The inhibition by Fr.E maybe due to nonspecific binding to protein. Yet in the reaction system contained about 50 fold amount of other proteins, the inhibitory effect of FrEA on xanthine oxidase still remained above 60%.