Effects of several pesticides on superoxide dismutase (SOD) activities of different rice varieties were studied. The results showed that SOD activities of almost all the herbicide treatments on different rice varieties increased during 15 days after treatment (DAT). SOD activity of rice plants reached a maximum at 10DAT, began to decline at 15 DAT and then recovered to the control level at 21 DAT. The SOD activity of rice plants at 2 days after the second application of pesticides (spraying with insecticide-bisultap or fungicide-jingganmycin at 22 days after herbicide treatments) (2 DAST) increased and declined at 6 DAST in comparison with that of the control, indicating that two applications of pesticides had a more serious impact on rice plants compared with one application. SOD activity of rice plants may be an index of rice plant resistance.