A magnesium oxide nanosheet assembly (NS-MgO) with high surface area (255 m(2)/g) and nanopore volume (0.30 cm(3)/g) was prepared by a pressure-assisted carbonation method at large scale. After loading of cobalt and molybdenum (CoMo) species and followed by sulfidation, the NS-MgO supported CoMo catalyst (Co-MoS2/NS-MgO) exhibits high activity (94.2%) and good nitrogen tolerance in the hydrodesulfurization (HDS) of dibenzothiophene (DBT), compared with a conventional gamma-alumina-supported CoMo catalyst (64.1%). These results are attributed to the difference in the basicity of the NS-MgO and gamma-Al2O3 supports. The large amount of the middle strong basic sites on NS-MgO can avoid the polymerization of Mo species and form small Mo oxide clusters. After sulfidation, the small MoS2 clusters with shorter lengths and less stacking formed on the NS-MgO contribute to an increase in the sites available for Co promotion, resulting in the Co-MoS2/NS-MgO catalyst with high HDS activity.