The electrical and mechanical properties in indium-tin-oxide films deposited on polymer substrate were examined. The materials of substrates are polyethersulfone(PES), polycarbonate(PC), polyethylene terephthalate(PET) which have gas barrier layer and anti-glare coating for plastic-based devices. The experiments were performed by rf-magnetron sputtering using a special instrument and buffer layers. Therefore, we obtained a very flat polymer substrate deposited ITO film and investigated the effects of buffer layers, in addition to the instrument. Moreover, the influences of an oxygen partial pressure and post-deposition annealing in ITO films deposited on polymer substrates were clarified. X-ray diffraction observation, measurement of electrical property, and optical microscope observation were performed for the investigation of micro-structure and electro-mechanical properties. They indicated that as-deposited ITO thin films are amorphous and become quasi-crystalline after adjustment of oxygen partial pressure and thermal annealing above 180 °C. As the results, we obtained 20-25 Ω/ of ITO films with a good transmittance (above 80%) under 0.2 % oxygen contents and vacuum annealing. Furthermore, using organic buffer layer, we obtained ITO films which have rather high electrical resistance (40-45 Ω/ ) but have improved optical (more than 85%) and mechanical characteristics compared to the counterparts.