Zinc oxide nanoparticles were synthesized by precipitation and modified sol gel methods. The influence of calcination temperature on morphology and crystallite size of ZnO was studied by varying temperature from 400 to 700 degrees C. The nano-structured ZnO particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDXS) and tranmission electron microscopy (TEM). The photo catalytic activity of as-prepared ZnO was evaluated by degradation of phenol under UV laser irradiation. The Photocatalytic degradation (PCD) efficiency of ZnO was found to decrease with the increase in calcination temperature due to agglomeration of particles and the increase in particle size. In addition to the effect of calcination temperature, the influence of various other parameters such as photocatalyst concentration, initial pH and the initial phenol concentration was also investigated to achieve the maximum PCD of phenol. The operational parameters show the expected influence regarding the efficiency of the photocatalytic degradation process. The results follow the pseudo-first order rate kinetics. (C) 2010 Elsevier B.V. All rights reserved.