Sputtering of aluminium doped zinc oxide thin films from a ceramic ZnO:Al target requires a controlled addition of oxygen to the sputtering atmosphere in order to obtain films with low resistivity and high transparency. In this paper the influence of the oxygen addition and of the substrate temperature on the structural, morphological and electrical properties of ZnO:Al films is investigated. The oxygen addition leads to a minimum resistivity when the oxygen content during sputtering is 0.2%. This small amount of oxygen not only improves the transparency of the films, it also induces to a significant grain growth as revealed by scanning electron microscopy. A further increase of the oxygen content leads to highly resistive films, due to a complete oxidation of the dopant Al. As expected, higher substrate temperatures from about 373 to 673 K improve the of crystallinity and hence the resistivity. The lowest resistivity achieved was about 1.2.10-3 Ωcm. At still higher temperatures the resistivity increases which seems to be due to an outdiffusion of sodium into the ZnO:Al films from the soda lime glass, compensating part of the donors.