This study was undertaken to investigate the putative antioxidant activity of the oyster mushroom Pleurotus ostreatus on CCl(4)-induced liver damage in male Wistar rats. Intraperitoneal administration of CCl(4) (2ml/kg) to rats for 4 days resulted in significantly elevated (p<0.05) serum levels of glutamic oxaloacetic transaminase (SGOT), glutamic pyruvate transaminase (SGPT) and alkaline phosphatase (SALP) compared to controls. In the liver, significantly elevated levels (p<0.05) of malondialdehyde (MDA) and lowered levels (p<0.05) of reduced glutathione (GSH) were observed following CCl(4) administration. Quantitative and qualitative analysis of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (Gpx) revealed lower activities of these antioxidant enzymes in the liver of CCl(4)-administered rats. An analysis of the isozyme pattern of these enzymes revealed variations in relative concentration presumably due to hepatotoxicity. When rats with CCl(4)-induced hepatotoxicity were treated with the extract of P. ostreatus, the serum SGOT, SGPT and SALP levels reverted to near normal, while the hepatic concentration of GSH, CAT, SOD and Gpx were significantly increased (p<0.05) and that of MDA significantly (p<0.05) lowered, when compared to CCl(4)-exposed untreated rats. Histopathological studies confirmed the hepatoprotective effect conferred by the extract of P. ostreatus. These results suggest that an extract of P. ostreatus is able to significantly alleviate the hepatotoxicity induced by CCl(4) in the rat.