Desulfurization from pyrite by Thiobacillus ferrooxidans in a packed-bed medium-recirculating bioreactor is examined. The concentrations of SO42- and Fe3+ eluted from the pyrite in the bioreactor increased with time, however, those became constant after a certain culture time. The higher concentrations of eluted products appearts inhibit is desulfurization by the bacteria. Inhibition of Fe3+ to the desulfurization process is higher than that of SO42-. Periodical exchange production in the medium with fresh medium in the bioreactor eliminates inhibition, which results in restart of the desulfurization process.