Interest in bifunctional catalysts, active in reactions such as hydrodesulphurisation (HDS) of hydrocarbon fractions, is growing in the last years. An improvement of CoMo/Al2O3 materials can be obtained by the introduction of other oxides during the sol-gel synthesis. This heavily affects the acid-base characteristics of the catalysts, while textural properties are less influenced. The catalytic performances change as well: a relationship between the density of acid sites and HDS activity has been found.