Angiostatin, a 38 ku fragment encompassing the four kringle region of plasminogen, has been identified and characterized to be a potent inhibitor of neovascularization and tumor metastasis. There is a strikingly similarity between tumor metastasis and embryo implantation. However, effect of angiostatin in the mouse blastocyst has never been reported. The results showed for the first time that angiostatin down-regulated the expression of matrix metalloproteinase-2(MMP-2), MMP-9, vascular endothelial growth factor family and its receptor, KDR, and up-regulated the expression of tissue inhibitor of metalloproteinase-1(TIMP-1) and TIMP-2 expression by binding with integrin αVβ3, suggesting that angiostatin may play a role in embryo implantation.