We systematically investigated the electrical transport properties of 2% Al-doped ZnO films deposited at different temperatures by rf magnetron sputtering method. For film deposited at 650 K, the temperature behavior of resistivity obeys the Bloch-Gruneisen law, i.e., it behaves as metal in electrical transport properties. While the tunneling effect across the grain boundaries governs the temperature behaviors of resistivity of the films deposited at 550 and 600 K. In addition, we found that the temperature dependence of resistivity of 4% Al-doped ZnO films deposited at 600 and 650K also exhibit metallic characteristics. These observations provide strong experimental supports for the validity of the ab initio band structure results of Al-doped ZnO. (C) 2012 Elsevier B. V. All rights reserved.