The effects of 80% ethanolic chlorella extracts (GPE) on carbon tetrachloride (CCl(4))-induced hepatic damage were investigated in Sprague-Dawley rats. The rats were orally treated with GPE (0.5 g/kg body weight) or silymarin (0.2 g/kg body weight) over four consecutive weeks with administration of CCl(4) (20% CCl(4), 0.5 ml/rat twice a week). The GPE had a significant protective effect against liver injuries, as well as oxidative stress induced by CCl(4), resulting in reduced lipid peroxidation and improved serum biochemical parameters such as aspartate aminotransferase and alanine aminotransferase. The reduced levels of glutathione, vitamin C, superoxide dismutase, and catalase in the CCl(4)-treated rats were significantly increased by treatment with GPE. Furthermore, the activity of GPE was comparable to the standard drug silymarin. In conclusion, chlorella may be useful as a hepatoprotective agent against chemical-induced liver damage in vivo.