Abstract: There are three iron sulfide minerals involving in gold-bearing ore, which take part in the process of microbial leaching, i.e. pyrite, pyrrhotite and pentlandite in order of gold content. And their bio-oxidation durations are therefore different because of their different distributions in gold-bearing ores. Experimental results showed that all of three minerals produced acidic substance, such as H2SO4. Pyrite is direct oxidized by bacteria and the cell content in solution is less than the other two minerals. Both pyrrhotite and pentlandite are also oxidized by Fe³⁺ besides direct bio-oxidation. Pyrite is more resistant to oxidation than the other two and its durability for oxidation is 3 times as long as that of the other two under the same conditions. It follows that the pyrite-rich gold concentrate should be less used in industrial applications. The bio-oxidation processes of the three single minerals were individually observed and analyzed, and their results can provide important data for reference to microbial leaching practice of complex gold concentrates.