A non-hemorrhagic metalloprotease (protease L4) was purified from the venom of Chinese Mamushi (Agkistrodon halys brevicaudus) by gel filtration and anion-exchange chromatography. Protease L4 has the molecular weight of 22 000 and its optimum pH was 8.5. The protein was stable in the pH range of 5-9 and below 40[deg ]C. The proteolytic activity was inhibited by metal-chelating agents and some metal ions. Calcium ion activated the activity dose-dependently, but had only a minor effect on the thermal and pH stability. L4 showed fibrinogenase activity, hydrolyzing only the A [alpha ] chain of fibrinogen. The protease cleaved preferentially at the N-terminal of Leu and His residues of some peptides.