SbOx thin films were prepared by the method of reactive dc magnetron sputtering; the optical properties and structural changes of the films were studied by using X-ray diffraction analysis and spectrometer respectively. By using the differential scanning calorimeter data of the amorphous film powder, measuring the peak temperature of crystallization at different heating rates, the crystallization kinetics of the thin films were studied.The results indicated that the as-deposited films were amorphous and there were two stages during the heat-induced crystallization. The first stage was the nanocrystallization of a primary phase antimony; the second stage was related to the formation of cubic Sb2O3 phase at higher temperatures. The Sb and Sb2O3 existed in crystalline films after annealed and there were much more Sb2O3 in 300 ℃ annealed films. The reflectivity of crystalline films was higher than that of the as-deposited films. The reflectivity of 200 ℃ annealed film was the highest in all crystalline films.