The complex refractive index shift of thermally-oxidized vanadium was measured over the spectral range from 0.26 to 0.7 mu m with varying temperature from 20 to 80 degrees C. The film of thermally-oxidized V is a mixture of different oxides with variable valences such as VO, V2O3, VO2, V2O5, and possibly others from the Magnaly's sequence : VnO2n-1, where n = 3-9. Over the temperature range under investigation only the oxide VO2 shows a semiconductor-metal transition so the dioxide fraction in the film defines the amplitude of the complex refractive index shift. Thus our investigation gives us information about film composition and emphasizes the important role of the neighbor order in forming the electronic structure. In addition, we studied (i) the kinetics of oxide film growth at different temperatures : 400, 450, 490 degrees C and (ii) the composition of the films oxidized at 450 degrees C by Auger electron spectroscopy (AES).