This article reports the effect of H2S exposure on the Fe-based water-gas shift catalysts and the surface and structural changes upon deactivation. Diffuse reflectance infrared Fourier transform spectroscopy was used to probe the interaction between reactants and catalyst surface before and after sulfur poisoning. X-ray photoelectron spectroscopy was used to examine the surface composition and oxidation states of the fresh and poisoned catalysts. Mossbauer spectroscopy and X-ray diffraction were used to investigate the bulk changes in the presence of H2S. A mechanism for catalyst deactivation with H2S was proposed by combining the reaction testing and characterization results. (C) 2009 Elsevier B.V. All rights reserved.