Indium tin oxide (ITO) films were synthesized on polymer (PES, polyethersulfone) at low temperature less than 100 degrees C by pulsed DC magnetron sputtering. The microstructure evolution of ITO thin film was investigated by employing the hydrogen gas in Ar discharge. The discharge behavior with hydrogen gas addition was analyzed by optical emission spectroscopy (OES) and microstructure change was investigated by XRD and TEM. It could be confirmed that the discharge with a mixture gas of hydrogen and At made an effect on the ionization of indium and oxygen gases as measured by OES and also significantly promoted the formation of crystallites of ITO in amorphous matrix. As a result, the resistivity of ITO film was significantly improved to 5.27 x 10(-4) Omega.cm at 0.026 Pa of hydrogen partial pressure below 100 degrees C in comparison with 2.65 x 10(-3) Omega.cm under hydrogen free condition. (C) 2008 Published by Elsevier B.V.