Nano and microcrystalline ZnO thin films were prepared on glass substrates using pulsed laser deposition technique under a vacuum of 3 x 10(-7) Torr at different laser power density. Composition analyses show that the films deposited at low laser power density have more structural defects than the film deposited at high laser power density. It confirms that the content of Zn in free-state decreased greatly at high laser power density. Atomic force microscopy analysis shows that the surface roughness of the deposited films increases with an increase in laser power density. X-ray diffraction analyses show that all the films are oriented along (0 0 2) direction independently on the laser power density applied. The structural quality increases with an increase in laser power density. It is due to the fact that the increase of laser power density leads to the enhancement of peak intensity. The increase of laser power density reduces the film transmission in the visible range of the spectra. The optical band gap value is found to be in the range from 3.42 to 3.39 eV. It shows that the optical band gap value decreases with an increase in laser power density. FTIR analysis shows that the hydrated oxide content in the deposited films decreases with an increase in laser power density. (C) 2009 Elsevier B.V. All rights reserved.