Coal, as one of the important energy sources in various industries, causes some of economical and environmental problems, because of its sulfur content. The most common forms of sulfur in coal are organic and inorganic (pyritic) sulfur. Organic sulfur is the sulfur in bound with carbon which is the integral part of coal matrix and cannot easily be removed, whereas pyritic sulfur is present in coal as mineral matter. Coal desulfurization is possible by different physical, chemical and biological methods. Among of this, biodesulfurization has a good potential to remove the fine-grained pyrite of high sulfur coals from economical and environmental points of view. In present research, a mixed culture of mesophile and also a mixed culture of moderate thermophile, acidophilic iron- and sulfur-oxidizing microorganisms were used to reduce pyritic sulfur from some of high sulfur coals in Parvadeh basin, Tabas, Iran. The effect of various parameters on biological removeal of sulfur and ash content of these coals was investigated. Also feasibility study of coal desulfurization by a heap bioleaching has been done, by design and establishment of a column bioreactor. In bioleaching experiment by mesophile microorganisms at shaking flasks, investigated parameters were consisting of nutrient medium type, initial pH and addition of ferrous sulfate. The optimum condition was Norris nutrient medium, pH=1 and 0.02 M ferrous sulfate addition, that occurred at 35°C, particle size of -500 µm, pulp density of 5% (w/w) and stirring rate of 150 RPM and resulted in 50% total sulfur reduction, 84% pyritic sulfur reduction and 35% ash content removal. It was indicated that Norris nutrient medium shows a better desulfurization rather than 9K medium. Also it was shown that by increasing pH from 1 to 2 and ferrous sulfate addition from 0 to 0.05 M the sulfur and ash content of residual coal would be increased. It was concluded that a high level of sulfate and jarosite precipitation occurred at initial pH=2 when 0.05 M ferrous iron added and 9K nutrient medium was used. In experiments by moderate thermophile microorganisms, investigated parameters were consisting of nutrient medium type, initial pH, particle size and addition of yeast extract. The optimum condition was Norris nutrient medium, pH=1.2, particle size of -500 µm and 0.02% yeast extract addition, that occurred at 45°C, pulp density of 5% (w/w) and stirring rate of 150 RPM and resulted in 64% total sulfur reduction, 98% pyritic sulfur reduction and 31% ash content removal. It was indicated that Norris nutrient medium has not a sensible difference with 9K medium in desulfurization. Also it was shown that by moving from pH 1.2 to 1.8 and from yeast extract addition 0 to 0.02% and from particle size of -150 µm to -500µm the sulfur and ash content of residual coal would not have a sensible difference. Bioleaching experiment in column bioreactor was occurred at 35°C, pH=1.25, Norris nutrient medium and 1 lit/min.m 2 solution flow rate. The reduction of 42% in total sulfur, 64% in pyritic sulfur and 12% in ash content was obtained. Keywords: Coal, Desulfurization, Mixed Culture, Bioleaching, Column Bioreactor.