Abstract: The present study was designed to evaluate the protective effect of Chlorella against liver oxidative damage induced by oral administration of 7,12-dimethylbenz[a]anthracene (DMBA) to female Wistar rats. Animals of protected groups were orally administered with dried powdered of Chlorella suspended in warm water at two selected doses; 0.5 and 1.0 g kg-1 b.wt. Water extract of chlorella tablets (Wakunaga of America Co., Ltd. Mission Viejo, CA, USA) was given to rats two weeks before DMBA administration and was continued for 15 weeks after cancer induction. Administration of DMBA (25 mg/rat) caused a significant increase of lipid and protein oxidations and significantly altered the levels of liver antioxidants. Treatment with chlorella extract has significantly prevented DMBA-induced oxidative changes in liver. Levels of MDA and P.carbonyl were significantly reduced after administration of chlorella extract. Chlorella has also restored normal level of indigenous antioxidants such as CAT, GSH, GST and SOD. The present results also show a high antioxidant activity of chlorella extract. It is therefore concluded that due to its potent antioxidant properties, chlorella modulates the DMBA-induced hepatic oxidative stress that is normally associated with induced-breast cancer in rats.