ITO films have been deposited onto glass substrates by rf reactive magnetron sputtering using an InSn (90-10) alloy target. After the deposition, the films were annealed in air at 500 degrees C for 30, 60, 90 and 180 min respectively. The film structure varies as the annealing time is changed. The films electrical properties show a strong dependence on the film structure. Although all the films show a preferred orientation along the (400) direction, the film which has a high (222) diffraction peak intensity has a high carrier mobility and a low resistivity.