A series of aluminum borates with various Al/B ratios were prepared by the precipitation method. These materials were used as the support of CoMo and NiMo catalysts. Hydrotreating of heavy Kuwait atmospheric residuum were carried out in a bench scale trickle bed reactor at 663 K and 7582 kPa. These catalysts were more active than the alumina-supported catalysts. An optimal boria content which gave the highest HDS and HDM activities was located around 4 wt% for both CoMo and NiMo catalysts. In addition, CoMo catalyst was always more active than NiMo catalyst provided the same boria content for both HDS and HDM reactions.