Abstract: The present invention relates to polypeptide having a primary structure of amino acid sequence shown by Sequence List Sequence No. 1 and DNA encoding for the polypeptide. The polypeptide is obtainable by following steps (1)-(3):Step (1): extracting small granule fraction of homocytes of horseshoe crab with a buffer containing protein denaturing agent and chelating agent,Step (2): subjecting said extract to reverse phase high performance liquid chromatography,Step (3): eluting by concentration gradient elution with a hydrophobic organic solvent.Also, the polypeptide is produced by chemical synthesis. The polypeptide has similar chemical structure to defensin and is useful as gargles, disinfectants, antiseptics or antimicrobials.