The sulfur effect of both thiophene and H2S on Mo2N/gamma-Al2O3 catalyst has been characterized by in situ FT-IR spectroscopy. CO adsorption was used to probe the effect of thiophene and H2S on the surface of the Mo2N/gamma-Al2O3 catalyst. The adsorbed thiophene has strong electronic interaction with the MozNly-Al2O3 catalyst and does not sulfide the surface of the catalyst at temperatures below 673 K, While in the presence of H-2, the surface of the Mo2N/gamma -Al2O3 catalyst can be partially sulfided by thiophene at temperatures as low as 373 K, simultaneously the adsorbed thiophene is decomposed or hydrodesulfurized on the catalyst. H2S has stronger interaction with the Mo2N/gamma-Al2O3 catalyst than thiophene does and can slightly sulfide the catalyst surface even at room temperature. The catalyst surface is deeply sulfided by an H2S/H-2 mixture at temperatures even about 373 K. The surface of the sulfided nitride catalyst can be only partially regenerated by a renitridation using NH3 at 873 K, indicating that some formation of sulfur species on the nitrided catalyst is irreversible. However, the nitrided surface can be completely regenerated when the catalyst is first oxidized and then renitrided, The sulfur effect on a reduced passivated MozNly-Al2O3 catalyst was also investigated.