Wurtzite-type MgxZn1-xO thin films were epitaxially grown at 550 degrees C on Al2O3(0001) substrate using low-pressure metal organic chemical vapor deposition (LP-MOCVD). The as-grown MgxZn1-xO shows poor optical quality with absence of the hand edge emission in the photoluminescence. Post-annealing in oxygen ambient has significantly improved the structural and optical properties of the films, with observation of strong near band edge emissions. Annealing inducing red-shift of the optical absorption for high xMg(x)Zn(1-x)O is due to a reduced Mg composition x, which agreed well with the observation of the XRDs. The annealing induced decrease in x has further been ascribed to Mg atom movement from the buried layer to the film surface, resulting in an inhomogeneous distribution of Mg atom across the film and an observation of lower xMg(x)Zn(1-x)O. (c) 2005 Elsevier B.V. All rights reserved.