Aim : To conduct the study on regenerative effect of rat undifferentiated embryonic stem (ES) cells against carbon tetrachloride (CCl4) induced liver damage in rats and determine their ability to differentiate into hepatocytes in the liver. Methods : Liver injury was produced by administration of CCl4 mixed with liquid paraffin. Liver injury induced by administration of CCl4, 0.5 mL /kg body weight, was injected into the peritoneum of rat twice a week for 2 weeks. Control animals received an equal volume of liquid paraffin. The dose of Embryonic Stem (ES) cells for the treatment damaged liver of rats was calculated according to the cell viability count and suspension was administered through intraperitonial route, 1 x 105 undifferentiated ES cells (0.1 mL of 1 x 106cells/mL solution),genetically labeled with GFP, were transplanted into the spleens 1 d after the second injection.