Laboratory feeding experiments using rice plants containing a synthetic cry1Ab gene derived from Bacillus thuringiensis Berliner (Bt) were carried out to study the effects of Bt rice-fed prey on the predator Propylea japonica (Thunberg). Plants were obtained from two homozygous transgenic Bt-cry1Ab expressing rice lines, Kemingdao 1 (KMD1) and Kemingdao 2 (KMD2), and their untransformed parental variety Xiushui 11 (XS11). The herbivorous prey species tested was the brown planthopper, Nilaparvata lugens Stål, one of most serious insect pests of rice and not targeted by KMD1 or KMD2. The concentrations of Cry1Ab toxin expressed in KMD1 and KMD2 plants and that of the toxin transferred to N. lugens feeding on these plants were determined by enzyme immunosorbent assay technique. Development parameters of P. japonica reared on KMD1- or KMD2-fed N. lugens were assessed in the laboratory. The results showed that the concentration of Cry1Ab in rice leaves and stems significantly increased from the booting to grain filling stage and subsequently decreased as the plants matured. Cry1Ab could be detected in nymphs and adults of N. lugens feeding on the Bt rice plants. Development time, pupation, adult eclosion, pupal and adult weight, and male-adult locomotive activity of P. japonica that had preyed on KMD1- or KMD2-fed N. lugens nymphs as larvae were not significantly different from those that preyed on XS11-fed nymphs. In short, our results indicate that the nontarget insect N. lugens and its predator P. japonica are exposed to Cry1Ab toxin from transgenic cry1Ab rice, but development of this predator was not affected by the toxin through tritrophic interactions.