The relationship between the molybdenum species of nitrided Mo/TiO2 catalysts and the HDS activity of the catalysts was studied by XPS and X-ray diffraction. The HDS of dibenzothiophene was carried out in a fixed-bed microreactor at 573 K and 10.1 MPa of total pressure, The 10.3% MsO3/TiO2 catalyst was nitrided by a temperature-programmed reaction with ammonia at 4 L h(-1) at various temperatures. The 1023 K nitrided catalyst held the highest TOF (based on CO adsorption). From XPS analysis, it was found that the 1023 K nitrided molybdenum catalyst was significantly difficult to sulfide the surface molybdenum species of the nitrided catalyst. The 773 K nitrided catalyst had more sulfur accumulation and less nitrogen release than the 1023 K nitrided catalyst. For the Mo/TiO2 nitrided above 973 K, titania was reduced and nitrided to form TiO and TiN but was not transformed to rutile, The molybdenum oxidation states of the nitrided Mo/TiO2 catalysts decreased with increasing nitriding temperature, and Mo2+ and Mo-0 ions are predominant on the surface of the 1023 K nitrided catalyst. The Mo2+ and Mo-0 ions were the most active for the HDS of dibenzothiophene.