The (In2O3)(77.34)(ZnO)(x)(SnO2)(22.66-x) (denote to IZTO-2) films with x = 13, 15, 17, 19wt.% were prepared on PET film with a 100-nm-thick SiO2 buffer layer by using RF-magnetron sputtering method, and their electrical stabilities were tested under various external stresses such as moist heat, temperature fluctuations and bending of substrate films. The lowest resistivity of 4.8 x 10(-4) omega center dot cm was observed in the IZTO-2 film of x = 17wt.% which also had such good properties as high electrical stability, surface uniformity, and high conductivity as compared with those of another (In2O3)(90)(ZnO)(7)(SnO2)(3) (IZTO-1) film. These results suggest that the optimum starting composition for IZTO film with high quality as a flexible transparent conducting oxide(TCO) film is In2O3 : ZnO : SnO2 = 77.34 : 17 : 5.66wt.%. The electrical stability of the optimum IZTO-2 film was greatly improved because the SiO2 buffer layer introduced between IZTO thin film and PET substrate acted as a blocking barrier to water vapour and organic solvents diffusing from the PET film and also as a buffer layer withstanding the bending damage.