An improved method of the purification of ricin D was investigated. Ricin was purified by gel-filtration through Sephadex G-75 at pH 8.0, followed by either CM-cellulose column chromatography at pH 6.5 or DEAE-cellulose column chromatography at pH 8.5. The homogeneity of the purified ricin was criticized by polyacrylamide gel disc electrophoresis.The purified ricin behaved homogeneous also in ampholine electrophoresis, indicating the isoelectric point of 7.34. Ricin thus purified was identical with ricin D in electrophoretical migration and toxicity. By the measurement of optical rotatory dispersion of the purified ricin, ORD constant, λc, Moffitt-Yang parameters, a0 and b0, were evaluated to be 235nm, -138 and -66, respectively.