To study the effect of toluene administration on the liver damage, rats were previously fed a low (casein 7%, LP) or standard(casein 20%, SP) protein diet and for four days toluene(50% in olive oil) was given at 0.2ml/100g body weight/day to the male rats, and then the degree of liver damage in toluenetreated animals fed LP were compared with those fed SP. The increasing rate of liver weight/body weight and the serum levels of xanthine oxidase to the control group were higher in rats fed SP than those fed LP. The decreasing rate of protein contents in cytosol, mitochondria and glycogen, glutathione contents of liver to the control group were higher in rats fed SP than those fed LP. In histopathological findings, the swelling of hepatic cell around the central vein was demonstrated in all the two groups toluene-treated rats. But the degree of swelling severity in hepatocytes was somewhat higher in rats fed SP than those fed LP. Therefore it is assumed that the degree of liver damage severity in toluenetreated animals was higher in rats fed SP than those fed LP.