Total RNAs were extracted from the venom gland of the Agkistrodon halys Pallas snake. The thrombin-like enzyme gene was amplified by RT-PCR, cloned, and its nucleotide sequences have been determined. The enzyme called pallase cDNA encodes 708 nucleotides, namely 236 amino acids. Based on the homology, the catalytic residues and disulfide bridges of pallase were deduced as follows catalytic residues, His(41), Asp(86) and Ser(182) and disulfide bridges, Cys(7)-Cys(139), Cys(26)-Cys(42), Cys(74)-Cys(234), Cys(118)-Cys(188), Cys(150)-Cys(167) and Cys(178)-Cys(203). The pallase expression plasmids under the control of the T7 promoter was constructed and the pallase was expressed in E. coli.