Investigation and evaluation of the activity of a metalloproteinase from B. atrox venom to better understand it is action mechanism. The purification procedure started with a gel filtration of the crude venom on a Sephadex G-75 column equilibrated and eluted with 0.05 M, ammonium bicarbonate buffer, pH 8.0. The resulting fractions were assayed for hemorrhagic activity by i.d injection in the dorsal region of mice, as well by SDS-PAGE. The active fraction was rechromatographed by ion exchange High performance liquid chromatography (HPLC) on a ES 502 N (Asahipak) column and the purified active fraction, named Batroxase 1, was submitted to chemical (Mr, pI, amino acid composition, N-terminal sequencing) and biological (clotting hemorrhagic and edema inducing activities) characterization. Batroxase 1 showed to be a monomeric protein, Mr 27,500 and pI 8.45. It did not show any free N-terminal amino acid residue along several degradation cycles. It is hemorrhagic activity was low (MHD 10 µg), in addition to a high edema inducing and no clotting activity. It was able to act upon the β-chain of fibrinogen and upon fibrin with a specific activity of 667 U/mg. Batroxase 1 is a new anticoagulant metalloproteinase from B. atrox venom since it is action is directed preferentialy toward the β-chain of fibrinogen, thus representing an experimental model for future investigations and applications in the field of thrombosis and haemostasis.