In this paper, vanadium nitride (VN) thin films have been deposited on Al substrates by reactive magnetron sputtering. Thermochromic VO 2 films have been obtained by air oxidation of VN samples performed at three temperatures (450, 525 and 550 C) at various durations (lower than 50 min). X-ray diffraction and Raman spectrometry of the VN oxidized films indicate that VO 2 and V 2 O 5 are the only phases produced during the oxidation process. Vanadium dioxide is the first oxide formed. It coexists with VN in a long period at 450 C or suddenly disappears at 525 and 550 C. Whatever the temperature, V 2 O 5 is exclusively detected after the total oxidation of VN. This oxide is detrimental to the thermochromic performance of films. The emissivity-switching properties of the oxidized films were analyzed by infrared camera in the 7.5e13 mm range. The comparison among all the samples exhibiting a thermochromic behavior shows that the maximum emissivity switch is independent of the oxidation temperature and the surface morphology of the samples. These results could open a new strategy in the investigation of VN oxidation as a method to obtain VO 2 , along with an insight into the correlation between surface morphology and optical properties.