In this work, it has developed two types of flexible substrates for organic devices. For this purpose, it was used the commercial high-performance thermoplastic, poly(ether imide) (PEI), and a natural and biocompatible polymer commonly used as artificial skin, bacterial cellulose (BC). PEI films were fabricated with good optical transparency in the visible range of spectra, flexibility and absence of pores, while the CB films were used as received. Thin films of indium tin oxide (ITO) were deposited on those films using rf magnetron sputtering in order to turn them electrical conductors for using in organic devices. The electrical resistivity of the modified substrates was improved by varying the ITO films deposition parameters. The lowest achieved resistivity was 3.27 × 10(-4) omega· cm for PEI substrates and 3.70×10(-4) omega·cm for CB substrates, comparable to the reference substrate (glass) 3.66 × 10(-4) omega· cm. In addition, due to the excellent thermal properties of PEI, ITO films on this material and on glass substrates were thermally treated to further improvement of its electrical properties. After this treatment, the resistivity values decreased to 2.88 × 10-4 ! · cm and 3.41× 10(-4) omega· cm for PEI and glass substrates, respectively. The obtained results are comparable or better than those obtained by other authors on different substrates, with and without heat treatment, establishing these materials as outstanding substrates for the development of flexible organic devices.