Indium tin oxide (ITO) is widely used to make transparent conducting films for various display devices. Recently, ITO films with low resistivities, low internal stresses, and high optical transmittance are required in relatively low-temperature processes for use in future display applications. However, to my knowledge, there are no reports of ITO films with both low resistivity and low internal stress having been successfully obtained in relatively low-temperature processes at less than 200°C. For this purpose, in this report, Indium tin oxide (ITO) films (260 to 280 nm in thickness, prepared by d.c.magnetron sputtering on a glass substrate at room temperature) were annealed in air, vacuum, and oxygen gas atmosphere. The structure of all the present as-deposited ITO films was not amorphous, but poly-crystalline. The electronic properties were measured by Hall effect measurements using the Van der Pauw method at room temperature. The internal stress was measured by using a thin-film X-ray diffractometer (XRD, Rigaku RINT 2500). It was found that, among the above post-annealing treatments, oxygen gas annealing significantly reduced both the resistivity and the internal stress in ITO films at fairly low temperatures of 100°C -150°C. Resistivities and internal stresses as low as 7 x 10@super-4@@ohm@cm and 38 MPa, respectively, were obtained by annealing in oxygen gas atmosphere at 100°. It was also revealed that the (111) crystal orientation becomes dominant and that whole grains grow dramatically as a result of post-oxygen-annealing, even at 100°C. It was tentatively concluded that the decrease of both resistivity and internal stress of post-annealed ITO films in oxygen gas atmosphere resulted from a large grain growth at relatively low temperatures. Finally, the optical transmittance of all of the post-annealed films in oxygen gas atmosphere was measured and found to be nearly 90% in the visible region of the solar spectrum.