Abstract: The cultivation of genetically modified plants may have the potential to alter microbial community structure and function in soils through root exudates and plant residues. Ammonia-oxidizing bacteria or denitrifying bacteria are the key microbes for nitrification or denitrification. A change in community structure of ammonia-oxidizing bacteria or denitrifying bacteria can affect the conversion and utilization of nitrogen in soil. The purpose of this study was to explore the possibility of transgenic rice to induce change in nitrogen transformation and N₂O emission in paddy soils. In the study, the abundance and composition of ammonia-oxidizing bacteria or denitrifying bacteria in paddy soils under straw return to soil under cry1Ac/cpti transgenic gene rice 'Kf8' or non-transgenic rice 'Mh86' were analyzed by real-time PCR and denaturing gradient gel electrophoresis (DGGE) based on amoA gene or nirS gene. The results showed that there were no differences in the abundance of amoA gene or nirS gene in the soil with returned transgenic rice 'Kf8' straw and non-transgenic rice 'Mh86' straw. The abundance of amoA gene in the 0-10 cm soil layer was significantly (P < 0.05) higher than that in the 10-20 cm and 20-30 cm soil layers under degraded transgenic rice 'Kf8' straw or non-transgenic rice 'Mh86' straw. The abundance of nirS gene in the soil increased with the time of returned straw to soil for either transgenic rice 'Kf8' or no-transgenic rice 'Mh86'. At the same time, the Shannon-Weiner index and composition of ammonia-oxidizing bacteria or denitrifying bacteria in the soil under degraded transgenic rice 'Kf8' straw were similar to those under degraded non-transgenic rice 'Mh86' straw. The composition of ammonia-oxidizing bacteria in the soil was significantly correlated with the time of rice straw return (P=0.002). Also the abundance of denitrifying bacteria was significantly correlated with the time of rice straw return (P=0.002) and depth of soil (P=0.024). The findings demonstrated that there was no significant effect of returned cry1Ac/cpti transgenic rice straw to soil on key microbial com-munities for nitrification or denitrification in soil. In terms of soil microbial community, there was no signiifanct effect of returned cry1Ac/cpti transgenic rice straw to soil on nitrogen transformation and N₂O emission in paddy soils.