Abstract: Toxicity of methamidophos to Nilaparvata lugens Stal (brown planthopper, BPH) was determined by the topical application method. The 4th instar larvae of BPH were treated with 5 doses of methamidophos. The survivals were reared on insecticide-free rice and divided into single-pair after emergence and the reproductive characteristics were observed and recorded. The results indicated that methamidophos could stimulate the population growth of BPH, but the stimulation was significantly different between the strains with different resistance levels to methamidophos. Field population (F) and resistant strain (R) had less stimulation ratio than that of susceptible strain (S), especially in R strain.