This paper presents the effect of post-heating temperature and atmosphere on the electrical and optical properties of ZnO:Al thin films prepared by the sol-gel method. The electrical properties of the n-type semiconductor thin films showed that for the final films, the values of carrier concentration ranged between 2.76 and 9.96 x 10(19) cm(-3), the Hall mobility values between 7 and 34.1 cm(2)/V s and the resistivity values between 2.9 x 10(-3) and 5.0 x 10(-2) Omega cm, depending on the processing conditions. For the thin film doped with 2 wt.% Al, preheated at 400 degrees C and post-heated for 1 h in air at 600 degrees C, a resistivity of 2.9 x 10(-3) Omega cm has been reached after annealing under a reducing atmosphere of forming gas. The optical transmittance spectra of the only post-heated films and of the post-heated and annealed films showed a good transmittance (75-90%) within the visible wavelength region and some small effects of Al-doping concentration and annealing treatment in forming gas. (c) 2005 Elsevier B.V. All fights reserved.