Molybdenum nitride thin films were prepared by N2 + implantation with acceleration energy of 20 keV and the ion dose of 3×1017 ions/cm2. The structural property and thermal stability of the films were investigated by XRD, AES, AFM and RBS. The crystal structure of N2 + implanted molybdenum thin films (Mo-N2 +) which had microcrystalline state was transformed to γ-Mo2N phase with a preferred (111) orientation after a post-annealing at 500 °C for 30min. However, a silicide reaction was not observed even after the annealing at 700 °C, which is due to the modification of the interface between Mo thin film and Si substrate by N2 + implantation. Also, Cu diffusion did not seem to be induced by the annealing at 700 °C for 30 min. The internal stress of the Mo-N2 + thin films during post-annealing at 600 °C for 30min was found to change from highly compressive stress to low tensile stress.