This paper deals with the biofilm formed on the surfaces of chalcopyrite during the bio-oxidation process. with microscopy techniques (scanning electron microscope, fluorescence stereo microscope and transmission electron microscope) and in situ chemical analyzes (energy dispersive spectrometer). SEM images showed that this type of structured community of Acidithiobacillus ferrooxidans was made up of some bacteria and floccules. Moreover, TEM images indicated that these bacteria were wrapped by EPS. However, almost no EPS can be found in the suspending bacteria in the solution. In addition, large amounts of jarosite and element sulfur were determined in the bio-oxidation process, and the biofilm was covered with the deposition. (C) 2008 Elsevier Ltd. All rights reserved.