Abstract: The present study deals with the effect of Melatonin (MT) against thioacetamide (TAX) induced hepatic damage in rats and to investigate the aging variation in the sequenced responses of injury, regeneration and capacity of recovery. For this purpose three groups of male Wistar rats were used. The first group aging 21 days, the second group aging 12 months and the third group aging 30 months. Thioacetamide treatment induced a significant loss of body weight and an increase in liver weight in all groups which was reversed with melatonin treatment. The histopathological alterations exhibited age-dependent changes related to liver injury and regeneration. Marked dilatation in sinusoids as well as the central and portal veins and necrosis of most hepatocytes were noticed especially in liver sections of adult rats. The cirrhotic features were reduced markedly in the liver of all animals treated with TAX and MT in comparison with rats treated with TAX alone. However, these improvements did not return to the normal liver structure of control group. From this study it can be concluded that melatonin participates in hepatocyte replication after toxin induced liver injury.