A cDNA encoding a guamerin has been cloned in E. coli and characterized. The guamerin is an elastase specific inhibitor with a low molecular weight of cysteine rich polypeptide isolated from Korean native leech, Hirudo nipponia. A cDNA encoding guamerin was identified by PCR amplification with degenerate primers based on its partial amino acid sequences of N-terminal and C-terminal. The deduced amino acid sequence revealed a different amino acid residue from that of guamerin. This cDNA had 71% local identity to cDNA of antistasin, factor Xa inhibitor derived from leech, Haementaria officinalis at the DNA level. The cDNA was expressed in E. coli and a 9-kDa protein was produced with inhibitory activity against neutrophil elastase as expected.