The support effects of Co-Mo sulfide catalysts on the activities for hydrodesulfurization (HDS) and hydrogenation (HYD) were investigated by preparing model catalysts. CoSx-MoS2 model catalysts were prepared by exposing supported Mo sulfide catalysts to a vapor Of CO(CO)(3)NO, followed by a second sulfidation. The supports used here were Al2O3, TiO2, ZrO2 and SiO2. XPS results showed that the Co sulfide species interacting with MoS2 particles are formed by using CO(CO)3NO as a precursor. On the basis of a proportional correlation between Co/Mo and NO/Mo ratios, it is concluded that the Co sulfide species are located on the edge sites of MoS2 particles, suggesting the formation of a CoMoS phase. The thiophene HDS activity was proportional to the amount of the Co species irrespective of the support for CoSx-MoS2/Al2O3, TiO2 and ZrO2, indicating that the Co species form catalytically active sites and that no real support effects are observed in terms of the specific activity of the Co species. The higher activity of the Co sulfide phase supported on SiO2 suggests that CoMoS(H) is formed on CoSx-MoS2/SiO2, whereas CoMoS(I) is formed on COSx-MoS2/Al2O3, Tio(2) and ZrO2. On the other hand, the Co species on TiO2, ZrO2 and SiO2 showed the identical specific activity for the HYD of butadiene. The Co species on Al2O3, however, exhibited a higher activity for HYD. The HDS and HYD reactions over the Co-Mo sulfide catalysts are affected by the support in different ways. The NO adsorption property of the CoSx-MoS2 model catalyst was also examined.