Since Bt cotton and corn were commercially planted in 1996, remarkable economic, ecological and social benefits have been obtained. However, ecological biosafety pertinent to their introduction has become a public concern, especially the potential impact of Bt crops on non-target organisms and evolution of resistance in target insect pests. The progress of laboratory and field assessment of Bt corn and cotton on non-target arthropods and resistance management of target insects were reviewed in this article. Research has shown that field populations of some non-target herbivorous insects in Bt crops may increase due to the removal of wide-spectrum insecticides. The pollen or nectar of Bt corn and cotton as food sources of honey bees or the natural drift of pollen onto food plants of silkworms have no direct or indirect detrimental influence on these beneficial insects as well as the monarch butterfly, Danaus plexippus. Bt cotton and corn may affect natural enemies indirectly by decreasing the population of lepidopteran insects that serve as hosts of parasitoids or predators. Population densities of predators in Bt fields were significantly higher than those in non-Bt fields treated with insecticides for control of target pests. However, population size and species richness of parasitoids might decrease due to lower density or poor quality of their host insects. There were no significant negative effects of Bt cotton and corn on the abundance and diversity of foliar and soil arthropod communities. Resistance monitoring demonstrated that resistance of target insects to Bt cotton and corn has not occurred in fields after 10 years of commercial use, either in large-scale farming system  as in the U.S. and Australia or in small-scale planting of Bt cotton in as China and India where several other non-Bt host crops of the target insects can serve as natural refuge. The absence of field resistance to date is presumed to be due to the implementation of refuge strategy in the developed countries and the unique cropping pattern in the developing countries. However, caution for resistance evolution continues to be warranted because resistance to Bt crops most likely remains a question of not “if" but “when". Therefore, future work should be emphasized on the impact of long-term and large-scale planting of Bt cotton and corn on non-target organisms and resistance evolution of target pests.