The dynamic change of superoxide dismutase(SOD)activity in common carp liver and muscle was studied after the fishes were statically exposed to 3.2, 5.6, 7.5, 10 and 18μg·L-1 Avermectin solution for 20 days. Results indicated that the SOD activity in liver and muscle, at the concentration of 3.2μg·L-1, were not significantly different from the control group (p >0.05). In 5.6μg·L-1 and 7.5μg·L-1 group, SOD activity increased strongly at first then decreased significantly compared with the control group (p<0....