The structural and optical properties of ZnO thin films deposited at various oxygen partial pressure and rf-power of rf magnetron sputtering were investigated. The sputtered ZnO films are mainly formed with the oxygen which was supplied from a sputtering gas; therefore the film stoichiometry can be controlled by the oxygen partial pressure and rf-power. From photoluminescence study, it was found that the wide emission band above 550 nm was observed due to an increase of oxygen vacancies when the ZnO film changed from O-rich to Zn-rich. The chemical stoichiometry of the film will help us to understand the formation mechanism of intrinsic defects in ZnO films. (C) 2011 Elsevier B.V. All rights reserved.