Transparent conducting Al-doped zinc oxide (ZnO:AI) films with good adhesion have been deposited on polyimide thin film substrates by r.f. magnetron sputtering technique at low substrate temperature (25-180℃). The structural, optical and electrical properties of the deposited films were investigated. High quality films with electrical resistivity as low as 8.5×10-4 Ω·cm and the average transmittance over 74% in the wavelength range of the visible spectrum have been obtained. The electron carrier concentrations are in the range from 2.9×1020 to 7.1×1020 cm-3 with mobilities from 4 to 8.8 cm2 V-1s-1. The densities of the films are in the range from 4.58 to 5.16 g/cm-3.