Abstract:The study was carried out with both random amplified polymorphic DNA (RAPD) polymorphism with which to analyze the genetic diversity of soil microbial communities and cultured-based microbiological method with which to analyze the numerical change of soil microbial communities, in order to find the difference between the soil planted with transgenic tobacco with the cecropin D gene and the soil planted with non-transgenic tobacco. The results from RAPD showed that the difference of genetic diversity related index of microbial communities in two kinds of soils was not significant. But the result from culturing and numbering showed that transgenic tobacco with the cecropin D gene significantly reduced microbial colony number. The decrement is: bacterial> fungus. Actinomycetes population was not affected. The results suggested that transgenic tobacco with the cecropin D gene may inhibit the pathogenic bacterial and the related rhizospheric microbes, but does not affect the microbial genetic diversity.