One of the best known of blood sucking animals is European leech which has been used in medicine for long time. There are many pharmacologically active substances, especially protease inhibitors such as hirudin, antistasin, bdellin, eglin, hirustasin, all of which have been isolated from Hirudo medicinalis. We have screened various protease inhibitors from the Korean native leech Hirudo nipponia and isolated trypsin inhibitory activity in the extract of acetone precipitation. The peptides were purified by Sephadex G-75 gel filtration, anion exchange, and reversed phase high performance liquid chromatography. The protein has a molecular weight of about 16 kDa estimated by SDS polyacrylamide electrophoresis and mass spectrometry. The amino acid residues of N-terminal region were sequenced. The result reveals that the inhibitor has 78% sequence similarity with bdellin B-3 that known for a leech derived strong trypsin inhibitor. Further studies are in progress to ascertain the complete sequence and functional properties of this interesting protein with the long range goal of application as a therapeutic agent.