The a-CNx films were deposited onto high-speed steel substrate by pulsed laser deposition at different nitrogen pressures. The tribological properties of the films in humid air and in vacuum were investigated using a ball-on-disk tribometer under various loads. The composition, microstructure and morphology of the films, wear tracks and paired balls were characterized by energy dispersive X-ray analysis (EDXA), X-ray photoelectron spectrum (XPS), Raman spectroscopy and scanning electron microscopy (SEM). With increasing the deposition pressure, the fraction of sp(3) C bond reduces, the fraction of trapped nitrogen increases and the friction coefficient of the films declines both in humid air and vacuum. The friction coefficient of a-CNx film decreases with increasing normal load. The tribological performances of the films in humid air are better than those of in vacuum. A transferred graphite-like tribo-layer is observed from a-CNx film to the paired ball for both environments. (C) 2009 Elsevier B. V. All rights reserved.