Abstract: Laboratory bioassay, pot and field experiments on the action mode, toxicity to instar, application technique and control effect of pymetrozine against brown planthopper (BPH) Nilapabata lugens (St?l) were conducted. The impact of pymetrozine on N. lugens natural enemies, Cyrtorhinus lividipennis (Reuter) and spider Agelena difficilis (Fox), was investigated. The results show that pymetrozine influences BPH through not only contact poisoning, but also a strong systemic action. LC50 values after 168 h of pymetozine application against the 1st and 3rd BPH nymphs are respectively 14.99 mg·L^-1 and 13.08 mg·L^-1, significantly lower than those against the 5th and adult nymphs. The results from the pot experiment indicate that control effects of pymetrozine are high when pots contain water layer. After 15 days, control effects exceed 95% in young BPH larva under 25% pymetrozine WP at 300 g·hm^-2, 450 g·hm^-2 and 600 g·hm^-2 with sustained paddy water layer. Further studies show that pymetrozine is moderately toxic to C. lividipennis (Ⅲ class), and C. lividipennis number decreases after pymetrozine application. Pymetrozine is safe to spiders (Ⅰ class), with insignificant impact on spider population after spray. This study therefore lays the scientific basis for rational use of pymetrozine.