Potent kininase activities were found in Japanese mushrooms. Especially Tricholoma conglobatum (shimeji, in Japanese) contained 40-334 kininase units/g and the enzyme was purified by water extraction, ammonium sulfate fractionation, diethylaminoethyl (DEAE)-Sephadex A-50 chromatography and Sephadex G-100 gel filtration. The final preparation gave a single band in disc electrophoresis and its kininase activity, that was expressed in terms of μg bradykinin degraded in 1 min at 30°, was 480 units/E₂80. This value was extremely potent, so this enzyme could be expected as a useful agent on the clinical purposes or other investigations of kallikrein-kinin system. The sites of action of this enzyme on bradykinin molecule were investigated by examination of 1-dimethylaminonaphthalene-5-sulphonyl (DNS)-modified products, which were liberated from bradykinin by this enzyme, on thin layer chromatography. It cleaved Gly⁴-Phe⁵ and Pro⁷-Phe⁸ bonds and the former bond was split more easily than the latter one.