Indium tin oxide (ITO) films were prepared by rf magnetron sputtering under two conditions: (i) at substrate temperature Ts from room temperature (RT) to 350° C, (ii) with additional post-annealing in vacuum at 400° C for 30 min in comparison of their crystalline structures, and electrical-optical properties of the films deposited. From the experimental results, it is found that, under the first condition, the crystalline structures and the electrical-optical properties of the films are improved with the increasing Ts. Under the other condition, i.e. with the additional post-annealing, the films exhibit higher degree of crystallinities and better electrical-optical properties. Under the two deposition conditions, inter-relation between electrical-optical properties and the crystalline structure is observed clearly. However, even under the same annealing condition, it is observed that improved properties of the films are different, depending on their deposition temperatures, which implies that an initial stage of the ITO film before annealing is an important factor for the film's properties improved after annealing. The resistivity of 2.33 × 10−4 Ωcenterdotcm can be achieved at Ts of 350° C after annealing.