Oriented (100) aluminium nitride thin films grown on silicon wafers (100) and other substrates, were deposited at 330°C by the metal-organic PECVD process. The oxidation behaviour in air of these films was studied at temperatures from 500°C to 1300°C by X-ray diffraction, scanning electron microscopy and Auger electron spectroscopy. Two textural changes occur: granular and porous textures at 900°C and 1100°C, respectively. These correspond to the amorphous Al2O3 and the crystalline α-alumina formation. Infra-red absorption spectroscopy shows that the oxidation effectively starts at 600°C and reveals an oxynitride phase between the amorphous Al2O3 coating which is formed, and the AlN remaining.