Abstract: A superoxide dismutase from leek plasma has been purified to homogeneltyby ammonium sulfate fractionation, Sephadex G-200 gel filtration and DEAE-Sephacelchromatography. 2. 4 mg purified enzyme was obtained from 500 g leaves. The specificactivity of the purified enzyme is 13000 U/mg protein. The enzyme is copper/zinc superoxide dlsmutase as assayed by its sensitivity to Inhibitors: KCN and H₂O₂. The molecularweight of the enzyme is about 30900 dations as assayed by Sephadex G-200 gel filtration, that of the enzyme subunit is about 15 900 dations as tested by sodium dodecyl sulphate-polyacrylamlde gel electrophoresis. The N-terminal of the enzyme is alanine astested by dansyl chloride. The enzyme exhibits one absorption maximum in the ultraviolet at 260 urn and another in the VISible region at 680 urn. The result of experimentsshows that the enzyme has good heat stability.