Thin CrAlCuN films with a composition of 21.5Cr-18.6Al-5.6Cu-54.3N (at.%) were deposited on steel substrates by the cathodic arc plasma deposition, and oxidized for up to 50 h in air. They consisted of alternating crystalline CrN/AlN nano-multilayers where Cu was incorporated. At 800 degrees C, a thin Cr2O3 layer formed. At 900 and 1000 degrees C, an outer Cr2O3 layer and an inner (α-Al2O3, Cr2O3)-mixed layer formed. Copper diffused outward to a small extent during oxidation. The film had good oxidation resistance, owing to the formation of the protective Cr2O3 and α-Al2O3.