Pursuit of ever-increasing storage density has lead to a steady reduction in head-disk separation which requires protective coating as thin and as hard as possible. It has been found that the internal stress affects micro-tribological properties of CNx film. In this study, thin hard CNx overcoats with different internal stress were synthesized by an ion beam assisted deposition method. Nanoindentation was used to evaluate the micro/nano mechanical properties of CNx film. The resultant load-displacement data was analyzed and it was found that the internal stress does affect the elastic modulus and hardness of CNx film according to the magnitude and type of internal stress. A finite element method was used to simulate the nanoindentation process and to examine the dependence of hardness and modulus on internal stress. Experimental results were compared with calculated results.