The characterization and hydrodenitrogenation activity of 3-methyl pyridine have been obtained. The results from the characterization techniques (X-ray diffraction (XRD), temperature-programmed reaction (TPR) and XPS) were used to illustrate the structure, surface reduction properties and the role of Ni metal in the reaction. The NiMoNx/gamma -Al2O3 catalyst is more active than a Mo2N/gamma -Al2O3 catalyst with the same MoO3 loading. Mo2N, Ni3Mo3N and Ni metal are formed in the NiMoNx/gamma -Al2O3 catalyst; moreover, the synergy among them is probably responsible for the high activity of NiMoNx/gamma -Al2O3 catalyst. The addition of Ni metal enhances the reducibility of Mo2N/gamma -Al2O3 phase and also promotes the KDN activity. The reasons for reduction before reaction and the surface ion state changes during reduction are illustrated by XPS techniques.