Abstract: The insect populations in the fields of insect-resistant transgenic Bt cotton(BT) and in the fields of conventional non-transgenic cotton(CV) in the coastal agricultural region of Jiangsu Province were surveyed and systematically compared in the year of 2004—2005.Results show that the insect community structure in the Bt fields differed sharply from that in the CV fields.The populations of the Lepidopterous pests,such as cotton bollworm,corn borer,diamond bollworm and cotton leaf caterpillar,decreased significantly in the BT fields,while the populations of non-target pests with piercing-sucking mouthparts,such as leaf bugs,cotton spider mites,cotton aphids and whiteflies,increased obviously.Much more predators,such as spiders and ladybirds,and much less parasitiods of Helicoverpa armigera were observed in the BT fields.The findings of the present study and others suggest that the effects of insect-resistant transgenic Bt cotton on insect population in cotton fields were relatively steady in recent years.