A cysteine protease from excretion-secretion products of adult Philippine Fasciola gigantica was purified to homogeneity by sequential gel filtration and anion exchange chromatographies, FPLC Resource Q anion exchange chromatography and then characterized biochemically. The molecular weight was estimated at 26 kDa by SDS-PAGE. It exhibited marked increase in proteolytic activity in the presence of dithiotreitol, slight activity with phenylmethyl sulphonyl fluoride but was totally inhibited by cysteine protease inhibitors, iodoacetic acid and leupeptin. Optimal activity was observed at pH 4 and at temperature of 35oC. It was stable at pH 4.5 to 5 when stored at 4oC. The enzyme was able to hydrolyze bovine serum albumin and bovine immunoglobulin G but not gelatin and hemoglobin at acidic pH. In addition, it was antigenic. This cysteine protease from adult Philippine F. gigantica may have potential use in diagnosis and prevention of ruminant fasciolosis.