Objective:To investigate the effect of matrix metalloproteinase-9 on the expression of caspase-3 and its possible mechanisms. Methods:The model of 70% hepatic ischemia-reperfusion was established in SD male rat. Total 48 SD rats were randomly divided into three groups(n = 16): sham operation group(S group),ischemia-reperfusion group(I/R group) and doxycycline treated group(DC group). After 3 hours of reperfusion,the enzyme levels in serum were examined, including ALT,AST,TNF-α and MDA. The expressions of MMP-9 and Caspase-3 were determined in immunohistochemistry. Results:After ischemia-reperfusion,the levels of ALT,AST,TNF-α and MDA expression in I/R group was significantly higher than those in S group. After treatment of oral doxycycline,the all above abnormal parameters were retrieved remarkably(P < 0.05). In the I/R group,MMP-9 and caspase-3 expressions increased,comparing with that in S group,while its expression decreased in the DC group,comparing with that in I/R group. Conclusion:The low expression of MMP-9 reduces the release and infiltration of inflammatory cells,inhibits caspase-3-mediated apoptosis of liver cells.