Differences in the population of culturable microorganisms and the enzymatic activities between soils amended with Bt-transgenic rice straw and non Bt-transgenic rice straw,respectively,were invest igated under laboratory conditions No significant differences(p<0.05) were observed in CFU(colony forming units) of culturable bacteria,act inomycetes and fungi between the two soils Although some apparent differences were observed in the populations of ammonifying bacteria,nitrogen fixing bacteria and cellulose-decomposing bacteria in the middle of the incubation,they did not last long Responses of various soil enzymes to the incorporation of Bt-transgenic rice straw and non Bt-transgenic rice straw varied No significant differences(p<0.05) in protease activities,neutral phosphatase activities,urease activities and respiration activities were found between the soil amended with Bt-transgenic rice straw and the soil blended with non Bt-transgenic rice straw Soil dehydrogenase was more sensitive than the other enzymes to amendment of the Bt-transgenic rice straw into soil Dehydrogenase activities in the soil amended with Bttransgenic rice straw were significantly higher(p<0.05) as compared to those in the soil with non Bt transgenic rice straw,and the apparent differences in the soil dehydrogenase activities,however,disappeared after incubation for 63 days Results indicate that the cry 1Ab toxin in straws of Bt-transgenic rice appears to be in toxic to the culturable microorganisms in upland soil.