A soluble thiol-dependent proteinase with molecular weight of 28 kDa was isolated and partially purified from Sparganum using ion exchange chromatography on DEAE-Triacryl M and Sepharose 4B affinity chromatography. This enzyme had maximal activity at pH 5.5 and showed inhibitor susceptibilities similar to the vertebrate acidic cysteine proteinases. One hybridoma cell clone, MASPC38 (Ig Gl) producing monoclonal antibody against partially purified cysteine proteinase was established. No cross reactivity was observed with six other parasite antigens. This antibody may be useful to detect the specific cysteine proteinase and/or circulating antigen of this parasite.