Superoxide dismutase(SOD) is an important member of the biological antioxidant system and one of the key enzymes that are responsible for the efficient removal of reactive oxygen species.As the first line of defense in the antioxidant system,it is almost ubiquitous in all forms of aerobic lives and is commonly distributed in the cytoplasm,mitochondria and chloroplasts.This paper reviews the progress in SOD research from its discovery,classification and distribution to its mechanism of action,molecular struc...