Abstract: In this paper，superoxide dismutase (SOD) was used as a template，and purification and modification were coupled to obtain more stable modified SOD with higher activity. SOD was mixed with DEAE-52 and Cu2+ chelating-sephadex G-75 without being washed immediately but modified by activated PEG5000 upon that solid-phase column，then washed specifically. The modification and purification of SOD were completed at the same time. Finally，the specific activity of PEG-SOD after IEC-modification was 9638.0 U/mg，with a purification factor of 1.87. It was modified at 35.3% of its free amino groups. And the specific activity of PEG-SOD after MCAC-modification was 9067.8 U/mg，with a purification factor of 1.755. It was modified at 40.9% of its free amino groups，retained 87.1% of enzymatic activity of native SOD. It is feasible to couple the purification and modification of SOD.And the coupling of MCAC and modification was better than this of IEC and modification.