A low resistivity and high transmittance Sn doped In2O3 (ITO) film was formed on a glass substrate by dc magnetron sputtering and lower sputtering voltage gave a lower resistivity film. At a sputtering voltage of −250 V, the resistivity obtained was 5.0×10−4Ω cm for room temperature substrate, 2.0×10−4Ω cm for 160 °C substrate, 1.9×10−4Ω cm for 200 °C substrate, and 1.2×10−4Ω cm for 460 °C substrate. At a sputtering voltage of −80 V, the resistivity was 1.3×10−4Ω cm for 200 °C substrate. A measurement of Hall effect shows that the decreased resistivity by lower sputtering voltage is not caused by the Hall mobility but by an increased carrier concentration.