Phosphorus solubilizing effects of four strains of phosphorus solubilizing bacteria (PSB) screened out of the red soil in Jiangxi Province were studied and compared through incubation in PVK solution containing AlPO₄ as phosphorus source. Results show that all the four strains displayed significant phosphorus solubilizing effects in the solution. Among the four, Strain B1 was the most effective in dissolving phosphorus. After four days of incubation, it dissolved 292.8 mg L^-1 phosphorus. Solution pH in all the treatments decreased to a varying extent from pH 7.0 to pH 3.2 ~ 4.7, during the incubation period. HPLC analysis shows that the presence of organic acids, varying in type and amount with the time of incubation, in the culture medium of all the strains. Oxalic acid and malic acid were found to the dominant organic acids in the culture medium of strain B1 and reached 5 mmol L^-1 in total concentration after 1 day of incubation. The experiment of adding organic acids to activate AlPO₄ indicates that B1 secreting organic acids to dissolve phosphorus is only one of the mechanisms of its phosphorus solubilizing capability. It was found that B1 favored a solution with pH varying between 5 and 9 and incubation under 30℃ and for a triangular flask (100ml), the most suitable content of medium was 30~40 ml. Identification of strain B1 shows that the strain is 99.9% in similarity to Bacillus thuringiensis in 16S rDNA genes.