Indium tin oxide (ITO) films were prepared on glass substrates at low temperatures by ion beam sputtering. Growth of the films was assisted by He ion beam irradiation. Optical transmission and electrical resistivity were then measured. In addition, FE-SEM was used to observe the films' microstructure, which was further studied by X-ray diffraction measurements. The relation between beam voltage, transmission rate and electrical resistivity is shown in this study. Finally, theoretical calculation of the Hall mobility and carrier density in ITO films by the Van der Pauw's method is discussed.