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 TiCl4 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 Al2O3-TiO2 supports preparation method. It was found that the formation of NiAl2O4 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. (C) 2003 Elsevier Science B.V. All fights reserved.