In the conditions of laboratory model experiment on composting of sewage sludge the influence of active phosphate-mobilizing bacteria on the release of water-soluble forms of phosphorus was studied. The experimental scheme included known active phosphate-mobilizing bacteria isolated from various ecological niches. The following components were used for composting: sewage sludge (SS), winter wheat straw and a suspension of phosphate-mobilizing microorganisms isolated from SSs of municipal treatment plants. The largest increase in water-soluble forms of phosphorus at the final stage of composting due to the introduction of Microbacterium barkeri. The greatest growth of water-soluble forms of phosphorus at the final stage of composting is provided by the introduction of Microbacterium barkeri LP-1, which can be explained by the greater adaptation of this strain to the substrate used in the experiments.