Abstract: Jarosite is a major secondary mineral formed in acid supergene environment by oxidation of metal sulphide．Thiobacillus ferrooxidans occurring extensively in metal sulphide ore district has an important effect on oxidation of metal sulphide and formation of secondary minerals．In order to discuss the effect of Thiobacillus ferrooxidans on the formation of jarosite，two parallel experiments were conducted for preparation of jarosite：chemical experiment and biologically mediated experiment．The compositions and morphological features of these two groups of jarosites have been investigated by means of XRD，SEM and EDS．The study indicates that full propagation of Thiobacillus ferrooxidans in the solution is beneficial to the formation of jarosite．The oxidation rate of Fe2+in the solution is probably the main factor that affects crystallization of jarosite．Thiobacillus ferrooxidarts induces a rapid crystallization of jarosite by increasing the supply rate of Fe2+ on the mineral surface．Jarosite mediated by Thiobacillus ferrooxidans has a better crystalline form than that synthesized by chemical method．