The growth kinetics of the bacterium Thiobacillus thiooxidans (HSS) was investigated and its metabolic acidic solution was used to bioleach phosphate rock. The bacterium HSS adsorbs on the surface of elemental sulfur particle and oxidizes sulfur to sulfuric acid to provide itself energy. The equilibrium between attached cells on sulfur surface and unattached cells in solution can be described with the Langmuir isotherm equation. The maximum adsorption capacity X-AM is 7.310 x 10(12) cells/kg of sulfur and the equilibrium constant K-A is 2.9110 x 10(-14) M-3/cell. In a batch growth process, the specific growth rate of the bacteria on sulfur, mu(A), and the growth yield, Y-A, are 2.874 day(-1) and 8.455 x 10(14) cells/kg of S, respectively. The bacterium shows the highest activity to oxidize sulfur at 30 degreesC. The dilute microbiological acid solutions produced by HSS were used to dissolve fluorapatite ore. The digestion conversions of phosphorus ranged from 24% to 100%. Fluorine ion contained in fluorapatite ore shows a significant effect on the biological activity of HSS.