Vanadium dioxide undergoes a transition at about 68 °C where the physical properties of the oxide, in particular the index of refraction and possibly the density, abruptly change values. In this work the indices of refraction of thermally grown films of vanadium dioxide on a vanadium substrate have been determined at room temperature and at 84 °C using the technique of ellipsometry. The index of refraction found for these films in this work is 2.82–0.317i at room temperature and 2.24–0.456i at 84 °C. In addition, our results indicate that there is a small increase in the thickness of each film upon heating through the transition.