Amorphous carbon-nitrogen films deposited by radio frequency-magnetron sputtering were annealed in vacuum for 30 min at temperatures between 300 and 700 degrees C, without any kind of sequential annealing. The annealing-induced modifications on the chemical composition of the films were followed by ion beam analysis (IBA). Raman scattering and infrared absorption spectroscopies were used to determine the microstructure modifications, while atomic force microscopy (AFM) was used to investigate the surface morphology. The internal stress of the films was obtained by measuring the bending of the substrate and the nanoindentation technique was used to measure the film hardness. Besides the nitrogen loss, determined by IBA analyses, Raman results suggested an increase in the size or in the number of the graphitic domains with the annealing temperature. AFM shows a decrease of the surface roughness as a function of the annealing temperature. The density, the hardness, and the internal stress of the films present a similar dependence on the annealing temperature, i.e., they increase with the temperature of the thermal treatment. The thermal treatment induces,a structural modification on the carbon-nitrogen films changing from a Soft paracyanogen-like material to a harder and more graphitic one.