NiMo catalysts supported on mixed TiO2-Al2O3 oxides containing between 0 and 22 wt.-% TiO2 have been prepared and characterized by temperature-programmed reduction (TPR), infrared (IR) and diffuse reflectance (DR) spectroscopy, BET and ammonia adsorption measurements. The samples have been tested in hydrodesulphurization (HDS) of thiophene. The spectral results show that the proportion of weakly bonded MoO42- groups is higher for NiMo/TiO2-Al2O3 catalysts compared to catalysts contained only molybdenum. The increase in TiO2 content in the mixed supports leads to a decrease of inactive NiAl2O4 spinel. An increase of Ni2+ ions in octahedral surroundings, included in a structure analogous to NiTiO3 is observed. Acidity shows the nickel-molybdenum surface interaction to be a result of the formation of a precursor of NiMoO4-like structure. The TPR results demonstrate that addition of titania into the support facilitates the Mo6+ reduction to Mo5+ and Mo4+. The influence of nickel on the molybdenum reducibility is revealed by a decrease of the temperature of reduction of the molybdenum species. The HDS activity of NiMo/TiO2-Al2O3 catalysts reaches a maximum at 17 wt.-% TiO2 due to formation of an active phase with an optimal composition of the oxidic precursors.