Abstract: The bioleaching of marmatite flotation concentrates by Acidithiobacillusferrooxidans was investigated.The leaching effects under the conditions of uninoculated, inoculated original strains, inoculated adapted strains were studied and the biooxidation rates of marmatite leached by the adapted strains for different pulp density values were determined.The experimental results on an orbital shaker showed that the adapted Acidithiobacillus ferrooxidans increased markedly the dissolution rate and the leaching ratio of marmatite under the leaching conditions of pH 2.0, temperature 35 ℃, 10% inoculating volume of microorganisms, 5% pulp density, <35.5μm particle size and rotating speed of a shaker 160r&#8226;min^-1.The increase of pulp density resulted in the decrease of the leaching ratio of Zn in marmatite minerals, and the increase of totally leached concentration of Zn²⁺ ions per unit time.