A precipitation technique at constant pH value was used to prepare a series of aluminum berates (ABs) with various Al/B atomic ratios. These samples have been characterized with respect to surface areas, pare volumes, and pore size distributions. These materials were used as the supports of Ni-Mo catalysts. Hydrotreating reactions of atmospheric gas oil (AGO) were carried out over these sulfided catalysts in a bench-scale trickle bed reactor; The results revealed that these catalysts are much more active than the conventional NiMo/Al2O3 catalysts on HDS reactions. They also demonstrate high aromatic;saturation capabilities; The high hydrodesulfurization activities of catalysts on aluminum borate supports can be rationalized by the presence of boron. Several effects may concur in these catalysts and facilitate their HDS activity. On one hand, it can increase the metal dispersions and the hydrogenation capabilities of the catalysts. On the other hand, it can increase the surface acidities and the cracking abilities of the catalysts. Both are beneficial to the HDS reactions of AGO. An optimum B2O3 content, which gives the highest HDS activity, is located around 4 wt%. The overdose of boron in the catalyst will cause a formation of B2O3 on the surface leading to a decrease in the activity.