Aluminum oxide films doped with Ce were prepared by the medium frequency reactive magnetron sputtering technique. Ce3+ content, the composition and the crystalline structure of the films were characterized by EDS, XRD and AES. The results show that the photoluminescence emission of these films shows peaks at the range of 374~405 nm which are associated with 5d to 4f transitions of Ce. The relative intensities of these peaks are strongly dependent on the amount of Ce incorporated in the films, and the substrate temperature during deposition. It is proposed that the light emission observed is generated by the luminescent center associated with cerium chloride molecular rather than the doped cerium ions (Ce3+). With the increase of Ce concentration, the photoluminescence peaks shift to lower energy, it would be associated with the existence of element chrorine in the films.