The present difficulties of ZnO in device applications urge deeper understanding of the growth kinetics in fabrication of high quality ZnO. To investigate the influence of buffer layers on the over-grown epitaxial ZnO layers, high-temperature (HT)-ZnO films with different buffer layers were grown on sapphire by molecular beam epitaxy, characterized by atomic force microscopy, photoluminescence and X-ray diffraction. Hexagonal MgO islands were observed on the low-temperature (LT)-MgO buffer layers. To improve the crystal quality, it is of great importance to optimize the buffer thickness and growth temperatures. The crystal quality of HT-ZnO grown on thinner MgO buffer layer (20 nm) is better than that on thicker MgO buffer layer (120 nm). And the surface and relative intensity of near band edge emission of sample with varied temperature grown ZnO buffer is better than other samples. (C) 2010 Elsevier B.V. All rights reserved.