Nitrogenated amorphous carbon films have been deposited by dual-facing-target sputtering, and their thermal stability has been investigated by means of X-ray diffraction (XRD), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS). The XRD analyses indicate a slower graphitization process in the CN films during annealing in comparison with the amorphous C films. The Raman measurements show that the sp(2) concentration increases through nitrogen incorporation, which in turns leads to a smaller layer expansion after annealing. Conductivity measurements further confirm this suggestion. The XPS results give the information of the existence of the strong covalent bonding between N and C atoms, which can slow down the tendency of the structural relaxation during annealing. The effect of nitrogenation on the formation of sp(3) bond is discussed tentatively in terms of coordination. These results suggest that the thermal stability of amorphous C films can be improved by N incorporation through reactive dual-facing-target sputtering.