To remove pyritic sulfur from coal, chemoautotrophic, acidophilic, iron-oxidizing bacterium Thiobacillus ferrooxidans was employed. Coal samples used in all the experiments were an anthracite coal obtained from the Han Yang Mining Company. The effects of various process variables（such as coal pulp density, salt concentration, particle size and initial cell density） on the pyritic sulfur removal rate has been determined. About 80-98% of pyrite(FeS₂) in coal could be removed by T. ferrooxidans within 11-15 days in a shake flask. The maximum pyritic sulfur removal rate increases linearly between 10 and 50%(w/v) of the pulp density and reaches a maximum level at 70%(w/v) of pulp density(1,117 mg-S/L·day). The optimum operating conditions are found to be a pulp density of 70%(w/v), particle size less than 0.42 mm, and initial cell concentration of 10⁹ cells/g-pyrite in coal.