To investigate how acetamiprid, a new insecticide, affects the activity of superoxide dismutase (SOD),catalase (CAT), and ATPase and the SOD isozyme patterns in two G- bacteria, E. coli K12 and Pse. FH2, and one G+ bacterum,B. subtilis. Methods The SOD, CAT, and ATPase specific activities of cell lysates were determined spectrophotometrically at 550 nm, 240 nm, and 660 nm, respectively, with kits A001, A016, and A007. SOD isozyme patterns were detected by native PAGE analysis. Results SOD and CAT activities in the tested bacteria increased significantly in a concentration-dependent manner after different concentrations of acetamiprid were applied. The activity of SOD in B. subtilis and Pse. FH2 was stimulated and reached the highest level after treatment with 100 mg/L acetamiprid for 0.5 h. For Pse. FH2, there was another stimulation of SOD activity after acetamiprid application for about 8.0 h and the second stimulation was stronger than the first.The stimulation by acetamiprid showed a relative lag for E. coli K12. Acetamiprid seemed to exhibit a similar effect on CAT activity of the two G- bacteria and had an evident influence on ATPase activity in the three bacteria within a relatively short period. Only one SOD isozyme was detectable in Pse. FH2 and B. subtilis, while different isozyme compositions in E. coli could be detected by native PAGE analysis. Conclusion Acetamiprid causes a certain oxidative stress on the three bacteria which may not only elevate SOD and CAT activities but also generate new SOD isozymes to antagonize oxidative stress.However, this oxidative stress lasts for a relatively short time and does not cause a long-term damage.