A series of molybdenum catalysts supported on MgO/Al2O3 (1: 1) mixed oxide were prepared and characterized by BET surface area, X-ray diffraction, temperature programmed reduction and oxygen chemisorption. The catalytic activities for hydrodesulpurization(HDS), hydrogenation(HYD) and hydrocracking(HYC) were determined using thiophene, cyclohexene and cumene as model compounds respectively. Results indicate that at 2-8% Mo loading, the catalyst is more dispersed and crystallite growth occurred beyond this range. The optimum metal loading for maximum oxygen uptake and catalytic activities for HDS, HYD and HYC was concluded to be 8%. The order of catalytic activity for HDS, HYD and HYC was: HYD>HYC>HDS. However, the Co promoted catalyst showed remarkable increase in both the HDS and HYD activity with no significant change in HYC activity, with the following order: HDS>HYD>HYC, the optimun Co loading being 3%.