Abstract: OBJECTIVE To investigate the protective effect of recombinant Urechis unicinctus fibrinolytic enzyme on rats with acute myocarchal ischemia. METHODS Recombined and expressed the Urechis unicinctus fibrinolytic enzyme. The fibrinogen plate method was used to estimated enzyme activity and the anticoagulation test was used to detected the anticoagulation effect in vitro. The rat model of acute myocardial ischemia was established to observe and determine the effect of recombinant Urechis unicinctus fibrinolytic enzyme on the weight ratio of myocardial infarction, serum biochemical indexes as lactate dehydrogenase(LDH), creatine kinase(CK), aspartate amino transferase(AST), blood coagulation index as prothrombin time(PT), partial thromboplastin time(APTT), fibrinogen(FIB), thrombin time(TT), activity of tissue plasminogen activator(t-PA) and tissue plasminogen activator inhibitor-1(PAI-1). RESULTS Compared with the model group, recombinant Urechis unicinctus fibrinolytic enzyme reduced the range of myocardial infarction, inhibited the increase of AST, LDH and CK, prolonged PT, APTT, TT, reduced FIB, increased t-PA activity and reduced PAI-1 activity, all had significant differences(P<0.01). CONCLUSION Recombinant Urechis unicinctus fibrinolytic enzyme can obviously enhance the fibrinolysis activity and reduce the coagulation time, which suggested that its inhibition of coagulation system and activation of fibrinolytic system may be one of its mechanisms for inhibiting thrombosis and anti myocardial ischemia. Recombinant Urechis unicinctus fibrinolytic enzyme can effectively prevent myocardial infarction, which can provide a theoretical basis for the next clinical application.