Zn1-xMgxO:Al thin films have been prepared on glass substrates by pulsed laser deposition (PLD). The effect of substrate temperature has been investigated from room temperature to 500 degrees C by analyzing the structural, optical and electrical properties. The best sample deposited at 250 degrees C shows the lowest room-temperature in resistivity of 5.16 x 10(-4) Omega cm, and optical transmittance higher than 80% in the visible region. It is observed that the optical band gap decreases from 3.92 to 3.68 eV when the substrate temperature increases from 100 to 500 degrees C. The probable mechanism is discussed. (C) 2007 Elsevier B.V. All rights reserved.