The antithrombotic action of catalase and chondroitin sulfatederivatives was studied on the rat arterial thrombosis induced by treatment of vessel withferrous chloride solution. The effect of native or chondroitin sulfate modified catalase,as well as the mixture of native catalase and free chondroitin sulfate in ratio which isequal to their content in conjugate was compared in respect to coresponding dosesaccording to active catalase content. The antithrombotic action of conjugate and itscomponent mixture is rather similar with each other and significantly exceeds the effectof native enzyme. The conjugate was the most effective in respect to retarding /prevention of arterial occlusion. The action of catalase preparations was altered thethrombus structure conducing blood stream retention at the low doses used. The directionsof further studies of antithrombotic activity for catalase, superoxide dismutase andchondroitin sulfate derivatives were founded.