The structural, optical and electrical properties of zirconium-doped zinc oxide have been investigated by first principle calculations. Three possible structures including substitutional Zr for Zn (Zr-Zn), interstitial Zr (Zr-i) and substitutional Zr for O (Zr-O) are considered. The results show that the formation energy of Zr-Zn defect is the lowest, which indicates that Zr-Zn defect forms easier and its concentration may be the highest in the samples. It is also found that as the proportion of Zr increases, the lattice constants increase while the optical band gap first becomes larger and then smaller, which are consistent with our recently experimental results. The electronic structure calculations display that as Zr-Zn defect is introduced into ZnO, the Fermi-level shifts to the conduction band, and there are excess electrons in the conduction band, which may be a possible reason of the good conductivity of Zr doped ZnO film. (C) 2008 Elsevier B. V. All rights reserved.