Objective:To investigate the effects of ischemic postconditioning on expression of liver nitric oxide synthase(NOS) in rat. Methods:The model of 70% hepatic ischemia reperfusion was constructed in SD male rat. Thirty two SD rats were randomly divided into three groups:sham group (SO group,8 rats),ischemia reperfusion group (IR group,12 rats) and ischemic postconditioning group (IPO group,12 rats). In group IPO,rats were treated as IR group,but at the onset of reperfusion,reflow was initiated with 10 s of full blood flow,followed by 10 s of re-occlusion,and repeated six times. After reperfusion for 3 hours,changes of ALT,AST and NO in different groups were compared. Reverse transcription-polymerase chain reaction and western blot were used to detct the expressions of NOS mRNA and protein respectively. Histopathological changes were observed by light microscope. Results:Compared with the SO group,ALT,AST and NO in serum were significantly higher (P < 0.01) than those in the other groups,and the mRNA and protein expressions of NOS were also obviously increased. Compared to the group IR,the levels of ALT,AST were significantly lower (P < 0.01),while NO was significantly higher(P < 0.01) in the IPO group. The expressions of NOS mRNA and protein were increased in the IPO group. Under light microscope,the group IR and IPO both showed typical pathological changes of ischemic-reperfusion injury,but the injury was extenuated in the IPO group. Conclusion:Ischemic postconditioning can protect liver from ischemic-reperfusion injury. The mechanism might be related with the induction of eNOS in tissue and the increase of NO in serum.