Abstract: Colonization dynamics of plant growth promoting Bacillus B96-Ⅱlabeled with GFP (B96-Ⅱ-gfp) in soils and cucumber plants were investigated via Green Fluorescent Protein Gene Label technique. The results show that B96-Ⅱ-gfp successfully colonizes in soils and cucumber plants. Total B96-Ⅱ-gfp populations are respectively 2.7×10⁴ cfu·g^-1 and 6.6×10⁴ cfu·g^-1 at 180 days after incubation in natural soils and usarium wilt pathogenic soils. B96-Ⅱ-gfp is detectable in the soil even at 360 days after incubation. Spatial colonization test indicates that B96-Ⅱ-gfp can colonize in the surface (0~4 cm), middle layer (4~8 cm) and lower layer (8~12 cm) of soil, and its population density increases with soil depth. Furthermore, B96-Ⅱ-gfp colonizes in different organs of cucumber plants, with a higher population in the interior than at the exterior surface. B96-Ⅱ-gfp population in roots is highest (7.2×10⁴ cfu·g^-1). Whereas B96-Ⅱ-gfp significantly reduces the population of cultured native soil microorganisms (e.g., fungi), it does not significantly influence the population of bacteria and antinomyces. The results further show that B96-Ⅱ-gfp increases the height, fresh weight and dry weight of cucumber plants. B96-Ⅱ-gfp exhibits a certain degree of control on Fusarium wilt. Labeled B96-Ⅱ-gfp is not significantly different from un-labeled B96-Ⅱ in terms of disease control and growth promotion.