Development of recombinant DNA technology has resulted in creating several lines of insectresistant crop plants. Various crops expressing Cry toxins derived from Baccillus thuringiensis (Bt) have been grown on a wide scale in the world, and they are playing an important role in pest control. However, one ecological concern regarding the potential effects of insectresistant GE plants on nontarget organisms (NTOs) has been continued to be debated. An increasing body of laboratory and field studies is now available on this topic. By summarizing previous research, we here briefly elaborated the general procedure for assessing nontarget effects of insectresistant GE plants, and analyzed the potential effects of Bt maize and Bt cotton on nontarget arthropods. The results indicated that the currently available Bt crops rarely had direct, acute toxicity on nontarget arthropods. In addition, the use of Bt maize and Bt cotton often resulted in reductions of insecticide application, thus increasing the abundance of at least some beneficial insects and improving their potential to provide natural control of specific pests at a reduced damage to the environment. Consequently, Bt crops can be a useful component of IPM systems to protect these crops from some targeted pests.