Aluminium oxide (Al2O3) thin films are widely used in mechanical, optical and microelectronic applications and have attracted more and more attention because of their excellent physical and chemical properties. However, Al2O3 has a variety of phases and their properties are different. So, the study of the effect of different structures on the luminenscence properties of Al2O3 is of significance in the practical application. The Al2O3 thin films are grown on silicon substrates by radio frequency (RF) magnetron sputtering and are annealed in the nitrogen gas at different temperatures. The structures and photoluminescence (PL) spectra of these films are compared with each other before and after annealing. Two fluorescence peaks are observed near 384nm and 401nm. Both fluorescence peaks are generated by the color center. With the increasing of annealing temperature, the crystallization of the films becomes better. At the same time, the position and intensity of the fluorescence peaks are changed correspondingly, too.