Abstract: With "Z16" and "SY321" as near-isogenic counterparts respectively, soil hydrolase and oxidoreductase activities were studied in a field experiment by planting transgenic Bt cotton "Z30" and transgenic Bt+CpTI cotton "SGK321". The results show that there are no consistent influences of transgenic Bt cotton and transgenic Bt+CpTI cotton on each soil enzyme activity. The activities of soil protease and dehydrogenase are both significantly reduced in the two transgenic cottons’ fields (P 0.05). Moreover, the activity of soil urease is significantly reduced in the transgenic Bt cotton field as well. The activities of soil phosphodiesterase, β-glucosidase, catalase and nitrate reducatse are significantly reduced in the transgenic Bt+CpTI cotton field, while those in the transgenic Bt cotton field are not obviously changed. Neither cotton cultivars nor transgnic events (difference of modified genes) have effects on soil acid phosphomonesterase and FDA hydrolysis activities; however, the effect on soil arylsulphatase activity is mainly from the difference of cotton cultivars.