ITO films were prepared by r.f. magnetron sputtering, and were annealed in ammonia, nitrogen and air atmosphere respectively. The annealing effects on electrical and optical properties of ITO films under different atmospheres were studied using X-ray diffraction (XRD), Hall Effect and UV-VIS-NIR spectrometer. The transmission of ITO films is greatly improved by the heat treatments in all atmospheres. The electrical properties of ITO films annealed in ammonia are better than in other two atmospheres.