Diamond-like carbon (DLC) coatings doped with different nitrogen contents were prepared by an ECWR-CVD deposition technique, and their chemical compositions, nano-mechanical properties and nano-tribological behaviors were characterized using Auger Electron Spectrometer and Hysitron Triboindenter, respectively. The results have shown that, higher nitrogen contents in the N-doped DLC coatings can be obtained by increasing the N2 flow rate in the reactive gas mixture. The nitrogen addition in the DLC coatings decreases evidently the nano-mechanical properties, including nano-hardness and reduced modulus. In addition, the depths for the scratched tracks produced during the scratch testing depend heavily on the nitrogen content in the N-doped DLC coatings, and, at the same applied loads, the higher the doped nitrogen content, the deeper the resulting scratched tracks. For the DLC coatings doped with different nitrogen contents, however, the frictional coefficients (LF/INF) deduced from nano-scratch testing at same loads are similar, and, therefore, seem to be independent of the added nitrogen content. (c) 2006 Springer Science + Business Media, Inc.