Abstract: The supports of magnesiumaluminum composite oxides were prepared by coprecipitation method using magnesium nitrate and aluminum nitrate as starting materials with ammonia solution as pH agent. The effects of magnesiumaluminum ratio, the kind of pH agent, pH value in the hydrolytic process, reaction temperature, calcination temperature, and crystallization temperature on the physicochemical characteristics of the magnesiumaluminum composite oxides were studied systematically in this paper. The selective hydrodesulphurization (SHDS) properties of the catalyst supported on the magnesiumaluminum composite oxides were investigated with the SHDS of residual fluid catalytic cracking (RFCC) gasoline as probe reaction. The results showed that the support of magnesiumaluminum composite oxides which was prepared at the ratio of magnesium to aluminum (Mg/Al) being 10, reaction temperature of 80℃ and the pH of 9.5, had proper specific surface area, uniform pore distribution and integrated crystal structure with high degree of crystallization. The catalyst supported on this kind of composite oxides performed well for SHDS of the RFCC gasoline.