Abstract: Al₂O₃ thin films were prepared by reactive DC magnetron sputtering with pure aluminum target at different O₂/Ar ratios.Exciting and Emitting spectra were obtained by using F-4500 fluorometer.Two peaks generated by the color center coming from the oxygen vacancy were observed respectively around 416 nm and 438 nm.With the increase of O₂/Ar ratio,the peak positions are not changed however their relative intensity ascends firstly then descends.This is related to the concentration of color center caused by the change of O₂/Ar ratio.X-ray diffraction spectra of the Al₂O₃ annealed and un-annealed in different temperature showed that the deposited Al₂O₃ thin films were amorphous in room temperature,until 400 ℃,Al₂O₃ crystal became crystal,and the crystallinity is improved with the increase of the annealing temperature.