In order to make clear the coordinatively unsaturated sites (CUS) of Co-Mo/Al2O3 sulfided at high pressure, the temperature programmed desorption of NO adsorbed on Co-Mo/Al2O3 sulfided at high pressure was studied by DRIFT method. The intensity of two IR bands (1835 and 1785 cm(-1)) of adsorbed NO on Co-Mo/Al2O3 decreased simultaneously up to 393 K. The higher frequency band disappeared at 393 K, while the lower frequency band remained even at 403 K. In the case of Mo/Al2O3, the intensities of two bands appeared at 298 K decreased monotonously with increasing temperature, and disappeared simultaneously over 433 K. In the case of Co/Al2O3, two bands disappeared simultaneously over 393 K. These results suggest that two kinds of nitrosyl species are formed on Co-Mo/Al2O3. One is dinitrosyl species adsorbed on CUS of Co, and the other is unidentified nitrosyl species. Comparing DRIFT spectra of Co-Mo/Al2O3 with those of a physical mixture of Mo/Al2O3 and Co/Al2O3, it is also suggested that the formation of the latter one correlates with the interaction between Co and Mo in Co-Mo/Al2O3. The unidentified nitrosyl species might be the key to explain the dependency of DRIFT spectrum of adsorbed NO on the pressure of sulfiding.