A gene encoding a novel serine protease designated as Harobin is cloned and identified from a sea snake venom gland bacteriophage T7 library. It has 265 amino acids and shares 50-70% similarity to terrestrial snake serine proteases. In addition to the 12 conservative Cys, it has three more Cys residues that may contribute to its higher enzymatic stability. Harobin is expressed in Pichia pastoris and purified. Recombinant Harobin exhibits an amidolytic activity, and specifically degrades Aalpha, Bbeta-chain of fibrinogen. It functions as a defibrase both in vitro and in vivo, and reduces thrombosis. Harobin prolongs the coagulation time and the bleeding time of mice and reduces the fibrinogen levels of rats as well. Meanwhile, intravenous injection of Harobin leads to the reduction of blood pressure in SHR rats. It results from the ability of Harobin that cleaves angiotensin I and release bradykinin from plasma kininogen in vitro and in vivo. These data suggest that Harobin is a novel defibrase and has a potential to be an agent for the therapy of thrombosis and hypertension.