Reducibility, sulphidability and hydrodesulphurisation (HDS) activity of molybdenum and molybdenum-nickel catalysts are related to the preparation method of alumina-titania supports. Supports containing 15 wt.% of titanium dioxide were prepared by hydrolysis of TiCl 4 on alumina surfaces (impregnation method) and by the coprecipitation method. The activity of the catalysts was investigated for the HDS of diesel oil fraction (1.05 wt.% S). The molybdenum distribution and the effect of nickel on the reducibility and sulphidability of the molybdenum catalysts depends on the Al 2O 3-TiO 2 supports preparation method. It was found that the formation of NiAl 2O 4 spinel was observed only on the support prepared by the coprecipitation method. The support obtained by this method is found to be of lower utility in the preparation of hydrodesulphurisation catalysts.