The research was conducted from February 2009 to June 2010 at the Southern Plant Protection Center using the brown planthoppers (BPH) collected at Cai Lay district, Tien Giang province and mass rearing by rice plants fertilized with different rates of nitrogen. This study aims to determine the influence of nitrogen on the insecticide tolerance of BPH (1) and identify the resistance index of BPH (RI) to Fenobucarb, Imidacloprid and Fipronil(2). The results showed that BPH developed different levels of tolerance to the insecticides after three generations rearing by young rice plants treated with different rates of nitrogen (from 0 to 200 kg Nlha). BPH rearing by young rice plants treated with high rate of nitrogen (200 kg/ha) showed increase in the tolerance to all three selected pesticides compared with lower nitrogen rates (0, 50, and 100 kg/ha). The tolerance trend iilcreased in the following generations of BPH when they were continually rearing by the young rice plants with high rate of nitrogen fertilizer. The resistance index of the tested BPH indicated that BPH collected at Cai Lay district appeared to be resistant to all three selected pesticides which have been widely used for BPH management in the Mekong Delta, including Fenobucarb, Imidacloprid va Fipronil. The resistance of BPH to the three selected pesticides was ranked as Fenobucarb Imidacloprid Fipronil.