By combining Swanepoel's theory and the Wemple-DiDomenico dispersion model, a simple method was established to determine the optical contants of the magnetron sputtered aluminum oxide films directly from the corresponding transmission spectra. The results showed that the magnetron sputtered aluminum oxide films exhibit the optical characteristics of high refractive index of 1.5661.76 (at 550 nm), negligible absorption in spectral region of 4001100 nm, as well as the direct band gap of about 3.914.2 eV. And the specific values of the optical constants strongly depend on the annealing temperature , which is one of the important technological parameters for the magnetron sputtered aluminum oxide films. Moreover, in the weak and medium absorption spectral regions, the calculated values of refractive indices are in satisfactory agreement with the results derived from the high-resolution Tek3000 film-characterization system, indicating the reliability and feasibility of the method in determining the optical constants of Al2O3films.