Transparent InO (Indium oxide) thin-film transistors fabricated by reactive ratio frequency (rf) magnetron sputtering at room temperature were demonstrated on glass and plastic substrates. The resistivity, transmittance, X-ray diffraction pattern, and surface morphology of the films prepared at a 50% oxygen partial pressure were investigated, the resistivity and the average transmittance of the films were 4.2¡Ñ104 £[-cm and 87 %, respectively. In addition, Indium tin oxide (ITO) and silicon nitride (SiNX) thin films were used as the electrode and gate insulator. The resistivity and the average transmittance of ITO electrodes were 7¡Ñ10-4 £[-cm and 85%. On the other hand, the maximum leakage current of less than 10-9A/cm2 was obtained for the SiNX layer at an electric field of 1 MV/cm. For the InO TFT on glass substrate with 6 £gm channel length and 20 £gm channel width, the measured saturation mobility, threshold voltage, on/off ratio and subthreshold swing are 9.39V-1s-1, 1.5V, 2.2¡Ñ107and 0.5 V/decade. For the TFTs prepared on plastic substrate, the measured saturation mobility, threshold voltage, on/off ratio and subthreshold swing are 8.19V-1s-1, 1.83V, 1.43.¡Ñ106and 0.8 V/decade, respectively.