Abstract: Chalcopyrite-pyrite bioleaching tests were performed with shaking flasks by Acidithiobacillus ferrooxidans. The research focused on the effects of basic salt mediums, pyrite-to-chalcopyrite mass ratio and mineral size distribution. It is found that chalcopyrite bioleaching can be promoted by pyrite. The leaching rate of copper in the iron-free 9K medium in pyrite-chalcopyrite bioleaching is 1.68 times as large as that in the 9K medium. The leaching of copper is better using a wide size range of minerals and the leaching rate of copper is related to the mass ratio of pyrite to chalcopyrite. When the mass ratio is 2:2, the highest leaching rate of copper is obtained to be 45.58%. The content of pyrite is of the essence in affecting the leaching rate level of copper. At a mass ratio of pyrite to chalcopyrite no more than 5:2 the oxidation of Acidithiobacillus ferrooxidans plays an important role in the bioleaching, but when the mass ratio is 10:2 the galvanic effect between the two sulphide minerals mainly influences the bioleaching. X-ray diffraction analyses of leaching residues indicate that the generation of jarosite in the iron-free 9K medium is less than that in the 9K medium, FeSO₄ in the 9K medium can be replaced by pyrite, the galvanic effect forms with chalcopyrite, and therefore the bioleaching efficiency of copper is increased.