Boron nitride films with aluminium added have been prepared by a dual-ion beam sputtering method. With increasing Al addition, the content of the cubic phase in the BN:Al films decreased monotonically, and the structure of the films changed to the hexagonal phase when the content of Al exceeded 3.2 at.%, while the compressive stress of 5.6 GPa and the hardness value of 60 GPa were reduced to 2 and 13 GPa, respectively The onset-temperature of oxidation of the cBN films with less than 2.3 at.% Al added was increased by approximately 150 K, compared with that of presently deposited pure-cBN film.