Intensifying effects of ferrous sulfate and pyrite on bioleaching of low-grade molybdenite concentrate were studied in this paper. The experimental results show that the oxidation dissolution of molybdenite can be accelerated with the addition of either ferrous sulfate or pyrite in bioleaching medium. Pyrite has better enhancing effect than ferrous sulfate, and the highest molybdenum leaching rate in pyrite-added solutions is 20.85%, increasing by 12.64% compared with that in 9K leaching system. Molybdenum leaching rate does not increase linearly with the increase of the addition of either ferrous sulfate or pyrite in each type solution. Great amounts of [NH4Fe3(SO4)2(OH)6] and[KFe3(SO4)2(OH)6] with different morphologies will be deposited on molybdenite ores when the additions of Fe from ferrous sulfate or pyrite exceed that from 9K leaching system by 0.5 times, and these deposits hinder the oxidation dissolution of molybdenite to some extent. Intensifying effects of ferrous sulfate and pyrite on bioleaching of low-grade molybdenite concentrate were studied in this paper. The experimental results show the the oxidation dissolution of molybdenite can be accelerated with the addition of either ferrous sulfate or pyrite in bioleaching medium. enhancing effect than ferrous sulfate, and the highest molybdenum leaching rate in pyrite-added solutions is 20.85%, increasing by 12.64% compared with that in 9K leaching system. Molybdenum leaching rate does not increase linearly with the increase of the addition of either ferrous sulfate Great amounts of [NH4Fe3 (SO4) 2 (OH) 6] and [KFe3 (SO4) 2 (OH) 6] with different morphologies will be deposited on molybdenite ores when the additions of Fe from ferrous sulfate or pyrite exceed that from 9K leaching system by 0.5 times, and these deposits hinder the oxidation dissolution of molybdenite to some extent.