A growing body of evidence supports lipid peroxidation as having a role in the pathogenesis ofliver disease. Although the probable cause of damage to human hepatocytes may be multifactorial, freeradicals have been implicated in a variety of liver diseases, particularly in the presence of ironoverload and toxic substances such as ethanol. Consequently, antioxidants, particularly those of plantorigin such as flavonoids, may help to reduce the risk of developing these diseases. Silybum (S.)marianum, a medicinal plant widely used in traditional European medicine for the treatment of liverdisorders, was evaluated for antioxidant activity. Thin layer chromatography and High PerformanceLiquid Chromatography analyses of crude extract of the plant confirmed the presence of a number offlavonoids reported in the literature. The antioxidant activity of these flavonoids was measuredthrough inhibition of lipid peroxidation and 1, 1-diphenyl-2- picrylhydrazyl radical scavenging. Thecrude plant extract showed marked antioxidant activity in both assays. These results suggest thatS. marianum contains flavonoids with antioxidant activity, capable of inhibiting or scavenging freeradicals, thus supporting its traditional use as a hepatoprotective agent.