Abstract: Snake venoms,especially those from the two subfamilies,Crotalinae and Viperinae,contained a lot of serine proteases.They were responsible for the hemorrhage,shock,or disorder of blood coagulation after envenomation.They acted,by activating,inactivating,or other converting effects,on almost all the components of hemostatic and fibrinolytic systems.Their sequences were homologous to trypsin-kallikrein serine proteases.Variation of primary sequences out of active center results in the difference of substrate specificities and the further difference of biological and pharmacological activities.Because of their common and unique properties compared to their physiological corresponding factors,snake venom proteases are proved to be an excellent model for the study of protease substrate discriminating mechanism.Furthermore,they have found an important position both in basic research and application of hemostasis and thrombosis in clinic.