In this work, nitrogenated a-C:H (a-C:H:N) films were prepared using the closed-field unbalanced magnetron (CFUBM) sputtering method on Si substrate with graphite target in a Ar+C2H2+N-2 plasma. We changed the ratio of nitrogen and acethylene gases used as reaction gas and applied the negative DC bias voltage of -200 V. The tribological properties of a-C:H:N films were observed. In the result, the increase of N-2 as the reaction gas in the plasma showed the growth rate and the N atomic ratio in the films increased markedly. Raman spectroscopy and X-ray photoelectron spectroscopy were used to investigate the chemical bonding structure and sp(3) fraction in the film. As a result, the film had the improvement of the physical properties such as the high hardness of 29 GPa, elastic modulus of 276 GPa and good adhesion of 35 N between a-C: H:N films and substrate. Also, N incorporated a-C:H films exhibited lower friction coefficient than a-C:H film without N. Consequently, the addition of N atoms in the a-C:H film was observed to improve the tribological properties of the film. (C) 2007 Elsevier B.V. All rights reserved.