Indium tin oxide (ITO) films were deposited on unheated PET substrates by DC reactive magnetron sputtering of In-Sn (90-10 wt%) metallic alloy target. Electrical and optical properties of as-deposited films were systematically studied by control of the deposition parameters such as working pressure, DC power, and oxygen partial pressure. The figures of merit are important factors that summarize briefly the relationship between electrical and optical properties of transparent conducting films. The formulae of T/R$\_$sh/ and T$^$10// R$\_$sh/ are expressed as a function of transmittance and sheet resistance. The best values of those figures of merit were approximately 38.6 and 8.95 ($ imes$10$^$-3/Ω$^$-1/), respectively.