Isoenzyme of superoxide dismutase(SOD) from kidney beans (Phaseolus vulgaris . L) seeds was purified by steps involving crude extract, chloroform-ethanol treatment, acetone precipitation, DEAE-cellulose chromatography and Sephadex G-75 chromatography. It had a specific activity of 127.45 U /mg. Its activity was strongly inhibited by H2O2 and KCN. It was proved that the purified enzyme was copper-and zinc-containing SOD. One of the isoenzymes was purified to homogeneity by discontinuous PAGE. The activity of this SOD could be changed by ultrasound treatment. The activity of SOD was increased after it was dealt with by ultrasound of suitable parameters. The ultraviolet absorption spectrum of SOD had no obvious change after treatment by ultrasound. Differential UV-spectra presented distinct positive peaks and negative peaks within certain wavelenth after ultrasound treatment.