ZnO:Al (ZAO) films were deposited on quartz substrates by dc magnetron reactive sputtering from a Zn target mixed with Al. The effect of substrate temperature and Al doping content on the structural, electrical and optical properties of ZAO films were investigated. It was observed that the (002) peak position of all films shifts to lower angle comparable to that of bulk ZnO due to the residual stress change with deposition parameters. The dependences of electrical properties such as resistivity, carrier concentration and Hall mobility on substrate temperature and Al doping content were measured. The minimum resistivity is 4.23×10−4 ω.cm with the carrier concentration of 9.21×1020 cm−3 and Hall mobility of 16.0 cm2v−1s−1. The visible transmittance of above 80% was obtained. The optical band gap was observed to increase with increasing carrier concentration. The possible mechanisms are discussed.