Polyphenol oxidase of Arctium lappa L. (edible burdock) has been purified by chromatographies on DEAE-cellulose, Sephadex G-75, and phenyl-Cellulofine to a homogeneous state as judged by SDS polyacrylamide gel electrophoresis. The molecular weight of the purified enzyme was estimated to be 31,000 by SDS-PAGE and 25,000 by gel filtration on TSKgel G2000SW. The optimum pH was 7.0 and the enzyme was stable at pH 7.0-9.0. The enzyme oxidized triphenols such as pyrogallol and phloroglucinol, and was completely inhibited by sulfide and cyanide, while it was neither affected by kojic acid nor N-hydroxyglycine (laccase inhibor). These results indicated that the enzyme had properties different from those of polyphenol oxidases from other sources such as mandarin orange and soybean.