The cDNA encoding human manganese-superoxide dismutase was amplified from the human liver cell (L02) total RNA by RT-PCR and sequenced. The human Mn-SOD cDNA was ligated into expression vector pET-24a(+) under T7 promoter. After 5 h induction with 1 mmol/L IPTG 800 mol/L Mn(2+) human Mn-SOD was highly expressed in E.coli BL21(DE3). The protein product was up to 50% of the bacteria total protein in soluble form and had specific SOD activity.