TiO2-Al2O3 composite supports have been prepared by chemical vapor deposition (CVD) over gamma -Al2O3 substrate, using TiCl4 as the precursor. High dispersion of TiO2 overlayer on the surface of Al2O3 has been obtained, and no cluster formation has been detected. The catalytic behavior of Mo supported on Al2O3, TiO2 and TiO2-Al2O3 composite has been investigated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methyl-substituted DBT derivatives. The conversion over the Mo catalysts supported on TiO2-Al2O3 composite, in particular for the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) is much higher than that of conversion obtained over Mo catalyst supported on Al2O3. The ratio of the corresponding cyclohexylbenzenes/biphenyls is increased over Mo catalyst supported on TiO2-Al2O3 composite support This means that the reaction rate of prehydrogenation of an aromatic ring rather than the rate of hydrogenolysis of C-S bond cleavage is accelerated for the HDS of DBT derivatives. The Mo/TiO2-Al2O3 catalyst leads to higher catalytic performance for deep HDS of gas oil. (C) 2000 Elsevier Science B.V. All rights reserved.