ZnS:Na thin films with (111) preferred orientation were deposited on glass substrates by vacuum evaporation method. The as-prepared films were annealed in flowing argon at 400—500 °C to improve the film crystallinity and electrically activate the dopants. The structural, optical and electrical properties of ZnS:Na films are investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance measurements and the four-point probe method. Results show that the as-prepared ZnS:Na films are amorphous, and exhibit (111) preferred orientation after annealing at 400 —500 °C. The PL emissions at 414 nm and 439 nm are enhanced due to the increase of the intrinsic defects induced by the thermal annealing. However, all the samples exhibit high resistivity due to the heavy self-compensation.