Ti-C-x-N-y thin films with different nitrogen contents were deposited by way of incorporation of different amounts of nitrogen into TiC1.02 using unbalanced reactive unbalanced dc magnetron sputtering method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and microindentation methods were used to investigate their phase configurations, nanostructures and mechanical behaviors in order to investigate their dependences on nitrogen content. The result indicated that the nitrogen content had a significant effect on phase configuration, nanostructure and mechanical behaviors of Ti-C-x-N-y thin films. The nitrogen-free TiC1.02 films exhibited a polycrystallite with nano-grains. On one hand, incorporated nitrogen substituted C in TiC1.02, producing Ti(C,N), and subsequently linked to the substituted C, forming C-N. On the other hand, the substituted C lined to each other, forming C-C. As a result, nanocomposite thin films consisting of nanocrystalline Ti(C,N) and amorphous (C, C-N) were produced. With further incorporation of nitrogen more C was substituted, accompanying with formation of more amorphous matrices and decrease of size of nanocrystalline Ti(C,N). The trend was enhanced with further increase of nitrogen content. A microhardness maximum of similar to 58 GPa was obtained in nitrogen-free TiC1.02 thin films. This value was linearly decreased with incorporation of N or increase of N content, and finally a hardness value of about 28 GPa was followed at a N content of similar to 25 at.%. Both elastic modulus and residual compressive stress values exhibited similar trends. (C) 2009 Published by Elsevier B. V.