After the dextran oxidized and activated by NaIO₄, two aldehyde groups were obtained by ring-opening reaction. Then, the addition reaction happened between activated dextran and SOD. The modified SOD could keep its enzyme activity effectively, and the stability of the modified SOD in acid, alkali, ethanol, and at high temperature was improved, respectively. It approved that the SOD was modified by dextran successfully through the Infrared spectrum analysis of its structure.