Objective：To analyze the activation mechanism of hepatic apoptosisrelated enzyme caspase3 during the early phase of liver regeneration in rats from the perspective of mitochondriamediated endogenous signal pathway.Methods: Thirtyfive male SD rats were randomly divided into 3 groups:model group \[70% partial hepatectomy (PH),n=15\],shamoperated group (n=15),and control group (n=5).The former 2 groups were further divided into 3 subgroups according to time after operation (3 h,6 h,and 24 h after operation,5 animals in each group).The animals in all groups were sacrificed and the liver homogenates were prepared.Using the fluorescence method,we determined the activities of hepatic caspase3 and caspase9 at 3 different time points after operation.The activity of glutathione peroxidase (GSHPx) and the content of NO were examined by enzyme immunoassay and nitrate reductase assay,respectively.Results: The activities of hepatic caspase3 and 9 both increased significantly compared with those of shamoperated group (P<0.01) at 3 h and 6 h after operation; the level of GSHPx was significantly decreased and the content of NO was significantly increased compared with those of the shamoperated group (P<0.01).Conclusion: Hepatic tissue is under oxidative stress during the early phase of liver regeneration,and the mitochondriamediated endogenous signal pathway is involved in the activation of caspase3.