The effects of thermal annealing on the surface morphology, composition and chemical bond structure of amorphous carbon nitride (a-CN) films deposited by de magnetron sputtering are reported. Atomic force microscopy (AFM) results show that thermal annealing can gradually change the surface structure of the films from a cauliflower-like texture eventually to a uniform granular texture. Fourier transform infrared absorption (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) have been used to characterise. the change of chemical bonding induced by annealing. By detailed analysis of both C Is and N Is photoelectron spectra, we have found that annealing can break the C-N bonds in the films and that the graphite-like C-N bonds are relatively more stable with the increase of anneal temperature.