Yellow earth, yellow rendzina and neutral purplish soil are typical soils for tobacco cultivation in Guizhou province and selected for studying community structures of microorganisms and their dynamics in the rhizosphere of flue-cured tobacco.During the growing periods of tobacco plants, the lowest count of bacteria was found at the rosette stage.Thereafter, it increased and peaked at the budding stage and then decreased till the mature stage.Actinomycetes and fungi showed a constantly increasing tendency from the rosette stage to the maturestage.The count of bacteria and actinomycetes in the rhizosphere differed between the soils, which are in the sequence of yellow earth > yellow rendzina > neutral purplish soil.In regard to the count of fungi, there existed the following tendency: neutral purplish soil > yellow earth > yellow rendzina.The microorganism population diversities and their dynamics in the tobacco rhizosphere also varied from soil to soil.In purplish soil, the number of dominant microbial populations in the rhizosphere was greater than in the other two soils, and the population diversities of bacteria and act inomycetes were even greater and more constant, suggest ing that the community structures of microorganisms in neutral purplish soil were more reasonable than in both yellow earth and yellow rendzina, which was probably related to the low incidence of tobacco bacterial wilt in the neutral purplish soil.