The results of the bioleaching process of the galena flotation concentrates from ZGH Boleslaw S.A. by Acidithiobacillus ferrooxidans bacteria have been presented. It has been recorded that the final level of conversion of S_S into S_SO4 in bioleaching process is about 48% and it is two-fold higher than in the control examinations. However, in the course of reaction there is a gradual passivation of the galena surface caused by sparingly soluble PbSO₄. The analysis of raw materials and the products by X-ray analysis proved that there are differences in the composition of reaction products after the process of bioleaching and control leaching. The tested bacteria have been identified on the surface of the examined raw materials by scanning electron microscopy.