Abstract: In this study,we examined effects of several proteinase inhibitors on implantation of mouse.We found that proteinase inhibitors soybean trypsin inhibitor (STI),ε-aminocaproic acid (EACA) and nitrophenol-p-guanidino benzoate (NPGB) could significantly inhibit mouse implantation when injected into uterine during pre-implantaion.We also found that NPGB could significantly inhibit attachment and outgrowth of blastocysts on the uterine epithelia cell monolayer when added into co-culture system,and STI and EACA only inhibited the outgrowth of blastocysts on the uterine epithelia cell monolayer.These results suggested that proteolytic activities were involved in implantation,some proteinases such as trypsin and plasminogen activator had important functions during trophoblast invasion.