Both the structural changes and frictional properties of CrN films, on two different substrate materials, were investigated as a function of both the effects of operating conditions and the effects of oxidization. The tribological behaviour reflecting these two kinds of effects is expressed by the tribological parameters of wear loss, the friction coefficient and the wear mechanism. The formation of oxide films affecting wear loss under various operating conditions was also examined. The wear losses, of chromium nitride and titanium nitride films, were compared at different specimen temperatures.