Undoped and Na-doped ZnO films were deposited by sol-gel method. The effects of sodium incorporation on structure,surface morphology and optical constants of the films were investigated. X-ray diffraction patts show the hexagonal wurtzite polycrystalline structure and that the sodium incorporation leads to the change in the structural characteristics of ZnO films. The SEM observations show that the surface morphology of the films is affected by the sodium incorporation. The transmission spectra show that the average transmittance of the films is above 85% in the visible range. The absorption edge initially blue-shifts and then red-shifts with the increase of Na doping content. The optical constants of these films were calculated using transmission spectra.Refractive indices of the films in the visible range decrease at first and then increase with increasing Na doping content.