Superoxide dismutase (SOD; EC 1.15.1.1) is an enzyme that protects against oxidative stress from superoxide radicals in living cells. This enzyme had been isolated, purified and partially characterized from muscle tissue of the shrimp Macrobrachium nipponense. The purification was achieved by heat treatment, ammonium sulfate fractionated precipitation and column chromato-graph on DEAE-cellulose 32. Some physiological and biochemical characterization of it was tested. The molecular weight of it was about 21.7 kDa, as judged by SDS–polyacrylamide gel electrophoresis. The purified enzyme had an absorption peak of 278 nm in ultraviolet region, and the enzyme remained stable at 25–45℃ within 90 min. However, it was rapidly inactivated at higher temperature. Treatment of the enzyme with 1 mM ZnCl2, SDS and 1mM or 10mM mercaptoethanol showed some increasing activity. However, the enzyme activity was obviously inhibited by 10mM CaCl2, CuSO4, ZnCl2 and 1mM CaCl2 and 10mM K2Cr2O7. SOD activity did not show significantly variation after incubated with 1mM CaCl2, EDTA and 10mM SDS. The enzyme was insensitive to cyanide and contained 1.03F0.14 atoms of manganese per subunit shown in atomic absorption spectroscopy, which revealed that purified SOD was Mn superoxide dismutase.