Ecological fitness characters of the brown planthopper increased proportionally with increase in nitrogen content of rice plants they were bred on. The nymphs survived better and had shorter life spans. Females weighed heavier, laid more eggs and lived longer. In addition, egg hatchability was significantly increased. Number of insects and dry mass from one pair of parents were also significantly higher in high nitrogen plants. Relationships between each of these characters with nitrogen content fitted the linear models well. These characters from insects reared on four successive generations in low, medium and high nitrogen regimes were also investigated. There was little between-generation difference in most characters, except for the population and its dry mass produced by one pairs of insects. This implies that in areas where nitrogen-rich crops are abundant over long periods, ecological fitness of the brown planthoppers are potentially higher and if natural biological control is compromised, the risk of extensive outbreaks are higher. Implications to sudden stoppage of insecticide use in these areas are also discussed.