The catalytic activity of alumina-supported molybdenum as well as cobalt-molybdenum nitrides for simultaneous hydrodesulfurisation (HDS) and hydrodenitrogenation (HDN) of vacuum gas oil (VGO) doped with quinoline was investigated. The relationship between nitriding parameters and activity was studied, Catalytic activities of nitrided and sulfided form of Mo as well as CoMo catalysts were compared. Nitrided Mo/Al2O3 proved to be significantly more active in the HDN than the sulfided form of this catalyst. Nitrided Mo/Al2O3 is also slightly more active in HDS than sulfided Mo/Al2O3. On the other hand, sulfidation of CoMo/Al2O3 leads to a catalyst with a higher HDS activity than nitriding. The HDN activities of both forms of CoMo are almost the same. Addition of cobalt to Mo/Al2O3 improves the HDS and HDN activities in its sulfided form, but has a negligible effect in the nitrided form.