In this paper, the investigation of optical properties of an indium-doped ZnO (IZO) thin films deposited on glass and polyethylene terephthalate (PET) by thermionic vacuum arc technique were done. Also, the surface, structural and electrical properties of deposited films were studied by an atomic force microscopy (AFM), field emission electron microscopy (FESEM), X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectrophotometer, interferometer and Hall effect system. Using a Filmetrics F20 thin film measurement system, the thickness values of the deposited IZO thin films were obtained as to be 110 nm and 190 nm on glass and PET substrates, respectively. All IZO films are in a polycrystalline structure. The estimated mean crystallite size values were recorded as 29.34 nm and 28.17 nm on the glass and PET substrates, respectively. The surface images of the FESEM analysis show growth of granular structure on the surface and the results are in good agreement with AFM results. Using UV-vis spectrophotometer and interferometer, the refractive index, reflectance, transmittance, absorbance and optical band gap of the deposited films were determined. The calculated optical band gap values of the films are obtained as to 3.64 eV and 3.55 eV for glass and PET substrate, respectively. The electrical measurements show that sheet resistance is dependence on the substrate materials. (C) 2017 Elsevier GmbH. All rights reserved.