A series of sulfided PtMo/ γ Al 2O 3 catalysts[ w (Mo)=9.0%] with different contents of Pt were characterized by using low temperature FTIR spectroscopy of adsorbed CO, while their HDS activity was investigated with thiophene as a model substrate. Experimentally, it was found that no existence of the bands related to the surface complexes of Al 3+ ←CO and Pt 0←CO→Pt 0 was observed at 77 K and that the rate of the thiophene HDS reaction(573 K) is well linearly proportional to the area of the Pt 0←CO band at 2 093 cm -1 with a higher extrapolated HDS rate compared to that of sulfided Mo/ γ Al 2O 3 catalyst at the zero content of platinum. On the basis of the results here, the conclusion may be made that the active monolayer phase of Pt Mo S may be formed over sulfided PtMo/ γ Al 2O 3 catalysts during the sulfidation process and that both Mo 2+ and Pt 0 sites for CO adsorption should be the active reaction centers of thiophene HDS. A series of sulfided PtMo / γ Al 2 O 3 catalysts [w (Mo) = 9.0%] with different contents of Pt were characterized by using low temperature FTIR spectroscopy of adsorbed CO, while their HDS activity was investigated with thiophene as a model substrate. Experimentally, it was found that no existence of the bands related to the surface complexes of Al 3+ ← CO and Pt 0 ← CO → Pt 0 was observed at 77 K and that the rate of the thiophene HDS reaction (573 K) is well linearly proportional to the area of ​​the Pt 0 ← CO band at 2 093 cm -1 with a higher extrapolated HDS rate compared to that of sulfided Mo / γ Al 2 O 3 catalyst at the zero content of platinum. On the basis of the results here , the conclusion may be made that the active monolayer phase of Pt Mo S may be formed over sulfided PtMo / γ Al 2 O 3 catalysts during the sulfidation process and that both Mo 2+ and Pt 0 sites for CO adsorption should be the active reaction centers of thiophene HDS.