Objective To observe the apoptosis in the livers of p21~(HBsAg/HBsAg) transgenic mice.Methods The liver of p21~(HBsAg/HBsAg) transgenic mice(6,12, 18,24 months) and corresponding p21~( / ) mice were assessed by flow cytometry.Result\ The apoptosis rate of the hepatocytes in p21~(HBsAg/HBsAg) transgenic mice was lower than that of wild mice of the same months.Conclusion\ HBsAg can inhibit apoptosis in liver cells of p21~(HBsAg/HBsAg) transgenic mice.