Indium-doped zinc oxide (IZO) polycrystalline thin films were grown on polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and as reference on 7059 Corning glass substrates at room temperature by radio frequency magnetron sputtering from a target prepared with a mixture of ZnO and In 2 O 3 powders. The structural, optical, and electrical properties of the films were analyzed and compared. The IZO polycrystalline films showed n-type conductivity. The electrical resistivity drops significantly, and the carrier concentration increases as a consequence of In incorporation within the ZnO crystalline lattice. In both cases the changes are of several orders of magnitude. The resistivity obtained was 3.1 ± 0.5 x 10 -3 Ω-cm for an IZO sample grown on PET with a carrier concentration of 3.1 ± 0.7 x 10 20 cm -3 , the best mobility obtained was 27.7 ± 0.8 cm 2 V -1 s -1 for an IZO sample grown on PEN. From the results, we conclude that n-type IZO polycrystalline films with high transmittance, high mobility and low resistivity were obtained on flexible transparent substrates.