The antioxidative effect of hot water extract of the mushroom Ganoderma lucidum on ethanol-induced free radical generation had been studied. In order to further investigate the hepatic and renal protective mechanism of Ganoderma lucidum, rates of lipid peroxidation were determined. The hot water extract of Ganoderma lucidum dose-dependently exhibited antioxidative effect on mouse liver and kidney lipid peroxidation; our results indicated that hepatic and renal homogenates have a higher malonic dialdehyde level in an ethanol administered group than in the Ganoderma lucidum treated group. It was concluded that the hepatic and renal protective mechanism of Ganoderma lucidum, might be due at least in part to its prominent superoxide scavenging effect. Ganoderma extract could protect the liver and kidney from superoxide induced hepatic and renal damages.