The effect of the support gamma-AL(2)O(3) modified with CaO by deposition-precipitation method on the structure, catalytic activity and selectivity of Mo and Ni-Mo catalysts for HDS was investigated. The resistance of the catalysts to deactivation by coke formation was also investigated. The samples have been characterized by means of XRD, DRS, XPS, Al-27 NMR, TPR, and specific surface area and pore size distribution. The reaction of thiophene hydrodesulphurization, carried out at atmospheric pressure, was used as a model reaction for estimating the activity of the catalyst samples. The obtained results show that the applied method of modification with CaO leads to the formation of support with mesoporous structure and a considerable higher mechanical strength than that of the pure gamma-Al2O3, Mo and Ni-Mo catalysts deposited on the modified support have higher HDS activity and resistance to coke formation. The presence of Ca2+ ions in the lattice of the support hinders the formation of crystallites OfMOO(3) and Al-2(MOO4)(3) phase. The higher catalytic activity of the samples with modified support is due to the higher degree of their sulfidation. (c) 2007 Elsevier B.V. All rights reserved.