Transparent conducting gallium-doped Zinc Oxide (ZnO:Ga) thin films were prepared on glass substrates by r.f. magnetron sputtering technique at low substrates temperature. The effects of post-annealing treatment on structural, electrical and optical properties of ZnO:Ga films were investigated. The results show that the annealing treatment leads to substational changes in the structural, electrical and optical characteristics of ZnO:Ga thin films. The electrical resistivity and the average transmittance of ZnO:Ga films were improved by annealing in vacuum ambient. The average transmittance increases from 85% to more than 90% and the electrical resistivity decreases from 1.13 x 10(-3) Omega cm to 5.4 x 10(-4) Omega cm after annealing treatment. (c) 2005 Elsevier B.V. All rights reserved.