Abstract: By means of SDS (sodium dodecyl sulfate)-polyacrylamide gel electrophoresis it was demonstrated that the fibrinolytic enzyme of Agkistrodon halys (Pallas) venom not only degrades the α chain but also degrades the β chain of human fibrinogen.A series of the fragments with different molecular weights,X′,Y′,D′,E′,could be observed electrophoretically on acid polyacrylamide gels after degradjng fibrinogen.The mechanism of the hydrolytic action of human fibrinogen by the fibrinolytic enzyme has been discussed.