We investigated indium- (In)-doping effects on the structural and electrical properties of a ZnO film. It was found that structural properties degraded as In-doping content increased, whereas electrical properties improved. We fabricated fully transparent and flexible InGaZnO4 thin film transistors (TFTs) using In-doped ZnO electrodes on polyethylene terephthalate (PET) substrate. The InGaZnO4/MgO-Ba0.6Sr0.4TiO3/3% In-doped ZnO/PET stacks exhibited a high transmittance of 80% in the visible range. The InGaZnO4 TFT with a 3% In-doped ZnO electrode showed a high field effect mobility of 1.04 cm(2)/V s and a moderate on/off ratio of 7.48x10(5).