Al–Sn co-doped ZnO thin films were fabricated onto quartz glass substrates by the sol-gel method. The surface morphology, electrical and optical properties at different post-deposition heating temperatures were investigated. The grains of preferred c-axis showed a well-mixed microstructure and the peak height was enhanced with the post-deposition heating temperature increasing from 400°C to 600°C. Doped films showed a preferential orientation along the (002) plane, while the preferential orientation changed to the (101) plane when temperature was higher than 500°C. The lowest resistivity 6×10–3Ω•cm was observed from samples made at 500°C, with an average 91.2% optical transmittance in the visible range. In this study, optical band gap of all the doped films were broadened, regardless of post–deposition heating temperature.