The structure changes of Au nano-particles supported on CeO2 were observed by using an analytical transmission electron microscope (TEM) with a specimen heating holder. The disintegration and growth of Au particles on CeO2 were successfully observed in the atomic scale. In situ observation of Au particles at elevated temperature reveals that the Au particles on CeO2 grow by Ostwald ripening process through surface diffusion. Iridium particles on CeO2 were also observed during the heating process for comparison. The growth mode of Au particles is quite different from that of In (C) 2007 Elsevier B.V. All rights reserved.