In this study, NbN thin films were deposited by reactive magnetron sputtering at different N₂ partial pressures and at room temperature. X-Ray diffraction analysis, transmission electron microscopy and atomic force microscopy were employed to characterize their phases, microstructure and surface morphology. Their microhardness and elastic modulus were evaluated using a microhardness tester and the effects of N₂ partial pressure on the phase formation, microstructure and mechanical properties of NbN thin films were investigated. The results show that there are clear effects of N₂ partial pressure on the deposition rate, phases, hardness and elastic modulus of magnetron sputtered NbN films. At a low N₂ partial pressure, the deposition rate is higher, while hcp β-Nb₂N and fcc δ-NbN coexist in NbN films. With the increase of N₂ pressure, the deposition rate decreases and the films are single-phase fcc δNbN; accordingly, the hardness and modulus reach peak values of 36.6 GPa and 457 GPa, respectively. A further increase of the N₂ partial pressure will cause hcp ε-NbN to appear in NbN films and then the hardness and modulus of films decrease.