To better understand the nature of carbon nanotubes supported Co-Mo catalysts (Co-Mo/CNTs) for selective hy-drodesulfurization (HDS) of fluid catalytic cracking (FCC) gasoline, studies are carried out using in situ Fourier transform infrared spectroscopy (FT-IR). The catalytic performances of Co-Mo/CNTs catalysts were evaluated with a mixture of cy-clohexane, diisobutylene, cyclohexene, 1-octene (60 : 30 : 5 : 5, volume ratio) and thiophene (0.5%, ratio of total weight) as model compounds to simulate FCC gasoline. The HDS experimental results suggested that the HDS activity and selectivity of Co-Mo/CNTs catalysts were affected by Co/Mo ratio; the optimal Co/Mo atomic ratio is about 0.4, and the optimum reaction temperature is 260 ℃. The in situ FT-IR studies revealed that 1-octene can be completely saturated at 200 ℃. In the FT-IR spectra of diisobutylene, the characteristic absorption peak around 3081 cm-1 for the stretching vibration peak of=C-H bond was still clear at 320℃, indicating that diisobutylene is difficult to be hydrogenated. As for the thiophene, no characteristic absorption peak could be found around 3092 cm-1 and 835 cm-1 when the reaction temperature was raised to 280 ℃, indi-cating that thiophene had been completely hydrodesulfurized. On the basis of FT-IR results, it can be deduced that thiopbene HDS reaction occurred mainly through direct hydrogenolysis route, whereas thiophene HDS and diisobutylene hydrogenation reaction over Co-Mo/CNTs catalysts might occur on two different kinds of active sites.