Abstract: The experiments were carried out with the dosages of 5 μg/kg,25 μg/kg and 100 μg/kg on 15 dogs for the anticoagulant action of defibrase from Agkistrodon acutus venom.The dogs were divided into three groups,5 dogs per group.Defibrase could conspicuously decreased the plasma fibrinogen of the 15 dogs (P<0.01).The decrease of fibrinogen induced marked anticagulant effect.The sample of blood was taken 5 hours after administration of defibrase and kept at 37℃ for 24 hours.The blood didnt coagulate.And the effect could last at least 24 hours.The spontaneous hemorrhagic complication and toxication were not observed.It showed that defibrase can play the anticoagulant role safely and distinctively.