This investigation has been conducted to study the protective effect of Thymoquinone against Diethylnitrosamine induced hepatic injury in rats. Twenty-eight of male Wistar albino rats (180-220g) were divided into four groups. The control group received intraperitoneal injection of saline (0.5 ml/kg) for seven days, Thymoquinone group was given thymoquinone (4mg/kg/day) for seven days by drinking water, diethylnitrosamine group was injected a single dose of diethylnitrosamine at the 5th day (intra-peritoneal, 100 mg/kg) thymoquinone+diethylnitrosamine group was given thymoquinone (4mg/kg/day) for seven days by drinking water and was injected a single dose of diethylnitrosamine at the 5th day (intra-peritoneal 100 mg/kg). The rats were anesthetized then livers were taken for process was followed for light microscopic research. The photo was taken by using light microscopy. The hepatocyte number were calculated using physical fractionator method. It was observed a significant decrease of the hepatocyte number in diethylnitrosamine group and thymoquinone+diethylnitrosamine group. In conclusion, diethylnitrosamine can cause liver damage and thymoquinone do not changed that diethylnitrosamine damage in liver.