The brown planthopper, Nilaparvata lugens Stl, is a classical resurgence pest induced by insecticides. In recent years, its outbreaks re\|occurred in China due to resistance to imidacloprid and the overuse of pesticides. The present study examined changes in the fitness of populations resistant and susceptible to imidacloprid under sublethal doses of deltamethrin and triazophos, using a life table method on two rice varieties, Xieyou 963 and Shenyou 1. The imidacloprid\|resistant population was obtained from Nanjing Agricultural University, which showed 932\|fold of resistance relative to a susceptible population. The susceptible population was obtained from the insect ecology laboratory of Yangzhou University, which had no contact with any pesticides over 10 years. Results from a multiple factor combination experiment showed that life table parameters of the resistant and susceptible populations varied with rice varieties, insecticide types and insecticide concentrations. The index of population trend (I) ranged from 13.1 to 484.3 in the resistant population and from 5.7 to 428.2 in the susceptible one. The relative fitness of 6 resistant populations in all 28 treatment combinations was significantly higher than that of susceptible ones, whereas other parameters of the resistant populations were not significantly different from those of the susceptible one. Thus, the resistant population appears to have reproductive advantages over the susceptible one under favorable environmental conditions.