Catalytic hydrodesulfurization plays an important role in the conversion of sulfur laden residual oils. Cobalt molybdate catalysts are more commonly used for this process. In the present study, a precipitation technique at constant pH value was used to prepare alumina support. This material has very narrow pore size distribution centered around the pore diameter of about 8 nm. It also has a large surface area and pore volume and, therefore, can be used as a support for CoMo RDS catalysts. The results of temperature-programmed desorption of ammonia indicated that this catalyst has higher surface acidity than the conventional catalysts. The high surface acidity could enhance the cracking ability of the catalyst. The RDS reaction results showed that the samples prepared by precipitation are more active and more stable than the conventional catalysts, at least in the first 72 h. The results can be attributed to its unique pore structure and high surface acidity.