The effect of both thermal annealing temperatures( 373 and 473) K for one hour in vacuum furnace on optical properties of ZnSe1-xAlx thin film doped with aluminum at x% (0, 2, 4, 6 and 8) was studied, which prepared by thermal evaporation method with 0.3μm thickness. The optical properties have been studied, and structure properties of ZnSe1-x Alx films have been studied by X-ray diffraction .The structure was polycrystalline with cubic structure with orientation (111), the films withx% 6 and 8and annealed at 373 K appeared new planes in (222) and (220) lead to appear the Al2Se3 phases. The observed results of the optical properties prepared films after heating treatment were decreased in absorption and increased in transmission. The value of the optical energy gap increased with increasing of thermal annealing from 373 to 473 K and decreasing with increasing aluminum concentration (x) from 2.85 eV to 1.99eV for all prepared samples.