A novel superoxide dismutase having the following properties: (a) action: the superoxide dismutase disproportionates two superoxide radicals to a hydrogen peroxide and a molecular oxygen; (b) substrate specificity: the superoxide dismutase acts on a superoxide radical: (c) optimum pH: the optimum a pH is about 8; (d) stable pH: the superoxide dismutase is stable at pH of 4.5 to 8.0 (when the superoxide dismutase is treated at 25°C for 60 minutes, the residual activity is at least 80%); (e) thermal stability: when the residual activity is measured after the heat treatment for 10 minutes at a pH of 7.8, the superoxide dismutase is stable at treatment temperatures of up to about 50°C, and the residual activity is 90% at a treatment temperature of 60°C, and 50% at a treatment temperature of 70°C; (f) molecular weight: the molecular weight is about 8.8 x 10⁴, as determined according to the gel filtration method; (g) absorption spectrum of ultraviolet and visible region: the maximum absorbance appears at about 280 nm, the minimum absorbance appears at about 250 nm and a shoulder appears at about 290 nm; (h) molecular extinction coefficient: the molecular extinction coefficient at 280 nm is about 1.45 x 10⁵ M⁻¹cm⁻¹; (i) inhibition: the activity is not inhibited by an addition of 1 mM potassium cyanide and exponential inactivation is caused with the lapse of time by an addition of 5 mM hydrogen peroxide; and (j) metal analysis: the superoxide dismutase contains 1.56 g-atoms of iron per mole of oxygen but does not contain copper and manganese; and a process for the preparation of the above-mentioned superoxide dismutase which comprises culturing a superoxide dismutase-producing strain belonging to the genus Norcardopsis in a culture medium to form and accumulate a superoxide dismutase in the culture medium, and recovering the superoxide dismutase from the cultured product.