Abstract: The toxicities of five commonly-used insecticides against different populations of rice brown planthopper, Nilaparvata lugens, fed on transgenic rice with cry 1Ab gene, KMD1 and KMD2 for different generations were measured and compared with those on non-transgenic parental rice variety, Xiushui 11. Activities of detoxification enzymes (EST and GST), target enzyme (AChE), and protective enzymes (SOD, CAT and POD) from different populations of N. lugens fed on KMD1, KMD2, and Xiushui 11 and the content of Cry protein were also detected. For all five insecticides tested, there were no significant differences in LD₅₀ values among different populations of N. lugens fed on KMD1 KMD2, and Xiushui 11 continuously in the laboratory and collected from the rice fields. For all six metabolic enzymes tested, there was no significant difference of enzyme activities among different populations of N. lugens fed on KMD1, KMD2 and Xiushui 11 for 1 and 9 generations in the laboratory or collected from the rice fields. The content of Cry protein was relatively stable in different populations of N. lugens fed on Bt rice, and was higher in N. lugens fed on KMD2. It was concluded that transgenic rice lines with cry gene, KMD1 and KMD2, had no significant effects on the susceptibility to insecticides and activities of metabolic enzymes of N. lugens.