Composite types of TiO2-Al2O3 supports, which are gamma-aluminas coated by titania, have been prepared by chemical vapor deposition (CVD), using TiCl4 as a precursor. Then supported molybdenum catalysts have been prepared by an impregnation method. As supports, we employed gamma-alumina, anatase types of titania, and composite types of TiO2-Al2O3 with different loadings of TiO2. We studied the conversion of Mo from oxidic to sulfidic state through sulfurization by X-ray photoelectron spectroscopy (XPS). The obtained spectra unambiguously revealed the higher reducibility from oxidic to sulfidic molybdenum species on the TiO2 and TiO2-Al2O3 supports compared to that on the Al2O3 support. Higher TiO2 loadings of the TiO2-Al2O3 composite support led to higher reducibility for molybdenum species. Furthermore, the catalytic behavior of supported molybdenum catalysts has been investigated for hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methylsubstituted DBT derivatives. The conversion over the TiO2-Al2O3 supported Mo catalysts, in particular for the 4,6-dimethyl-DBT, is much higher than that obtained over Al2O3 supported Mo catalyst. The ratio of the corresponding cyclohexylbenzene (CHB)/biphenyl (BP) derivatives is increased over the Mo/TiO2-Al2O3. This indicates that the prehydrogenation of an aromatic ring plays an important role in the HDS of DBT derivatives over TiO2-Al2O3 supported catalysts.