A recombinant plasmid was constructed by inserting a DNA fragment with the coding region of Cu/Zn-superoxide dismutase (Cu/Zn-SOD) cDNA from sweet potato, Ipomoca batatas (1) Lam cv Tainong 57, into the 3' end of the open reading frame of the glutathione S-transferase (GST) gene in an expression vector, pGEX-2T. The constructed plasmid was transformed into E coli XL1 Blue. Fusion proteins of Cu/Zn-SOD and GST (GST-SOD) were produced from the recombinant E coli. About 6mg of GST-SOD fusion proteins could be obtained from 1 dm(3) of cultural broth after induction with 0.075mmol dm(-3) Isopropyl-beta-D-thiogalactoside (IPTG). Lactose was not an efficient inducer. High cell density culture was performed by fed-batch fermentation using a glucose analyzer to control glucose concentration at 1 g dm(-3). The cell density of the fed-batch culture reached an OD600 of 30, the total amount of GST-SOD fusion protein was 100mgdm(-3) which is about 14 times more than that of the batch culture. Most of the fusion proteins were shown to be in an active monomeric form, and the molecular weight was estimated to be 45kDa by SDS-PAGE and 47kDa by gel filtration. The specific activity of the purified fusion proteins was about 1200mg(-1) and equal to 3200 unit per mg of SOD domain only.