Superoxide dismutases scavenge superoxide radicals and protect cells from oxidative stress. SOD gene of Bombyx mori nuclear polyhedrosis virus has been cloned by PCR, and is expressed in E.coli with the activity of SOD being 576.13 u/mL. DNA sequence analysis shows that SOD gene of BmNPV encodes 151 amino acids. The homology between BmNPV and AcNPV of the nucleotide sequences of SOD gene is 97.2%, and 56% between BmNPV and human SOD1.