The brown planthopper,Nilaparvata lugens (St?l), is the most serious insect pest of rice. It has developed high resistance to traditional insecticides because of their intensive use. Juvenile hormone (JH) analogs have been used successfully to control this species and other pest insects. However, the molecular mechanism of JH signaling is not well understood.Krüppel-homolog 1 (Kr-h1) is a transcription factor involved in the JH pathway. In this study, theKr-h1cDNA was cloned and characterized from N. lugens by rapid ampliifcation of cDNA ends (RACE) and reverse transcription PCR (RT-PCR). Its spatial and temporal expression proifles were examined by real-time quantitative PCR, and its function was also studied by RNA interference (RNAi). The open reading frame ofNlKr-h1 is 1833 bp encoding for 611 amino acids. The protein contains eight conserved zinc-ifnger motifs.NlKr-h1 was expressed at all life stages, with the highest mRNA level in the 4-day embryo.NlKr-h1 mRNA levels rose during each nymphal molt after the 2nd instar. In the adults, the mRNA level in males was signiifcantly higher than that in females of either the macropterous or brachypterous type. The highest expression was observed in the female midgut.NlKr-h1 was activated by juvenile hormone III (JH III) in the 3rd-5th instar nymphs. Disruption ofNlkr-h1expression by RNAi caused stunted wing development and malformations of both male and female external genitalia. Our ifndings suggest thatKr-h1may be a useful target for pest insect management.