Optical properties of vanadium dioxide (VO2) thin films, prepared under various deposition conditions by laser ablation, were investigated at 1.3 mu m wavelength. Optical constants, n and k, at 1.3 mu m were measured by ellipsometry. Not only the extinction coefficients, k, but also refractive indices, n, remarkably changed through the phase transition. The reflectances, r, and transmittance, t, were calculated From these n and k and their transition profiles in temperature were almost coincided with those directly obtained by the spectrophotometry. The analysis of the transition magnitude in reflectance revealed the clear relation between these values and the deposition conditions : the ambient oxygen pressure and the substrate temperature.