Mo(100)-c(2 x 2)-N, as a model surface for the real Mo2N catalyst, was prepared. The adsorption of CO and (NO)-N-15 on this model surface were studied by high-resolution electron energy loss spectroscopy (HREELS). It was found that CO and O-15 not only could be adsorbed on the top of the Mo sites but also could react with surface N sites to form surface NCO and N2O species, respectively. This indicated that both the Mo atoms and N atoms of the surface are ail active for CO and (NO)-N-15 adsorption.