The chemical and morphological changes induced in the pyrite surface by the leaching and bioleaching processes in the presence of catalytic Ag ions have been comparatively studied by means of X-ray photoemission spectroscopy, atomic force microscopy, and scanning electron microscopy. Core level photoemission spectra of the S(2p) and Fe(2p) peaks have revealed the formation of different oxides in the leaching and bioleaching processes. Bioleaching leads to the formation of higher valence oxides (jarosites) than those formed in the leaching process. These chemical changes are directly reflected in the surface morphology and particularly as an important increase of the surface roughness. Moreover, the inclusion of catalytic Ag ions in the leaching medium does not produce substantial modification of the topography, and the Ag is incorporated in little grains (similar to 0.1 mu m wide) which are spread along the surface. However, the presence of Ag in the bioleaching medium inhibits the formation of high valence oxides and leads to a different oxidation mechanism. The roughening of the surface due to the catalytic bioleaching is also significantly slowed down by the presence of Ag ions in the solution.