Abstract: A pot experiment with a transgenic Bt cotton BtXincai1 and an acceptor cultivar of Bt gene Xincai1 was conducted to investigate the effect of transgenic Bt cotton planting on the biological characteristics and nutrient contents in rhizosphere soil at different growth stages. Biological characteristics were assessed by measuring the number of culturable microorganisms and enzymes activity in rhizosphere soil. Results showed that Bt protein could be detected in the rhizosphere soil of BtXincai1, and reached the peak value of 56.14 ng/g at flowering stage of cotton growth. Compared with Xincai1, BtXincai1 stimulated the proliferation of bacteria and fungi. However, no significant effect on actinomycete was observed. BtXincai1 showed a significant inhibition effect on alkaline phosphatase activity and no significant effect on protease, urease and sucrase activity over the growing season, but a significant stimulation effect on dehydrogenase activity at fast growth stages. BtXincai1 had no significant influence on the content of organic matter, total N, available-N and K at seedling and flowering stages as well as available-P at seedling, but decreased the content of available-P at flowering stage significantly.