Objective：To detect expressions of matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-3（MMP-9/TIMP-3） in the endometrium of patients experiencing recurrent in vitro fertilization-embryo transfer（IVF-ET） failure and to explore the possi－ble mechanism. Methods：Expressions of MMP-9/TIMP-3 in endometrium at mid-luteal phase in 40 patients experiencing recurrent IVF-ET failure（experiment group） and 40 pregnant women with IVF-ET once a time（control group） were detected by immunohisto－chemistry SP. Results：Expressions of MMP-9 in experimental group were significantly lower than those of control group（P<0.05），but there was no significant difference in TIMP-3 expressions between both groups（P >0.05）. Conclusions：Recurren IVF-ET failure is possibly caused by lower expressions of MMP-9 in endometrium at mid-luteal phase.