The impacts of transgenic Btrice on target pests and their predators need to be clarified prior to the commercialization of Btrice. In this study, the percentages of folded leaves of three transgenic Btrice lines and non-transgenic parental rice line caused by Cnaphalocrocis medinaliswere studied over two successive growing seasons. In addition, the population densities, relative abundance and population dynamics of C. medinalisand four species of its natural arthropod predators were investigated at three sites in China. The results showed that rice line significantly affected the percentages of folded leaves and population densities of C. medinalislarvae. Significantly higher percentages of folded leaves were observed on the non-transgenic rice compared with the three transgenic Btrice on most sampling dates. Significantly higher densities of C. medinalislarvae and higher relative abundance of C. medinaliswithin phytophages were found on non-transgenic rice compared with three transgenic Btrice at different sites across the study period. The population dynamics of C. medinalislarvae were significantly affected by rice line, rice line×sampling date, rice line×year, rice line×sampling date×year. However, there was little, if any, significant difference in the relative abundance, population density and population dynamics of the four arthropod predators between the three Btrice lines and non-transgenic rice. The results of this study indicate that the Bttoxin in transgenic Btrice can effectively suppress the occurrence of C. medinalis, but has no significant effects on the occurrence of the four predatory arthropod species.