In the present paper, the nitrogen-doped ZnO thin films with variable doping levels were produced by using wet chemical process. These ZnO films were investigated by PL spectrum, Raman spectrum, optical reflection and XRD measurement. The XRD result showed that a new phase appeared in the heavy-doped ZnO films. In addition, the small shift of the Raman peak indicated that the stress existed in these ZnO films. This resulted in the disorder of the lattice of the ZnO film and the appearance of new ZnO phase. (C) 2010 Elsevier Ltd. All rights reserved.