The effect of KCl on the morphology, composition, optical and electrical properties of ZnO nanostructures obtained from aqueous solution method was investigated. Field emission scanning electron microscopy reveals that by increasing the content of KCl in the precursor solution, the morphology of the samples changes from one-dimensional ZnO nanorod arrays to two-dimensional dense films. This is accompanied by a decrease of the growth rate and an improvement of the crystal quality. After annealing at 550 degrees C, the optical band gap energy changed from 3.5 to 3.2 eV due to the decrease of Cl impurity, and the defect species had changed from vacancies of oxygen into interstitial oxygen ions. A possible mechanism for the morphology transformation is discussed. (C) 2008 Elsevier B.V. All rights reserved.