The toxicity of seven insecticides to the brown planthoppers of Jiulongjiang，Vietnam was evaluated with four bioassay methods. The orders of toxicity （value of LC50） to the brown planthoppers were fipronil＞pymetrozine＞ thiamethoxam＞ buprofezin＞chlorpyrifos＞imidacloprid＞isoprocorb with rice stem dipping and pymetrozine＞fipronil＞imidacloprid＞chlorpyrifos＞isoprocorb with topical application and fipronil＞pymetrozine＞thiamethoxam＞buprofezin＞chlorpyrifos＞isoprocorb＞imidacloprid with rice seedling dipping and fipronil＞isoprocorb＞chlorpyrifos＞thiamethoxam＞pymetrozine＞imidacloprid＞buprofezin with residual film. In conclusion, the toxicity of fipronil，pymetrozine and thiamethoxam to the brown planthoppers of Jiulongjiang，Vietnam was higher than that of buprofezin and chlorpyrifos， and the toxicity of imidacloprid，isoprocorb was the lowest. Furthermore, the toxicity of isoprocorb was the second highest and the toxicity of buprofezin was the lowest with residual film in seven insecticides.