A precise knowledge and understanding of the thermal stability of nanowires is a prerequisite for the reliable implementation of nanowire-based devices. Single crystalline Au nanobelts with {1 1 0} surface either in free standing arrays with identical crystallographic orientation or lying on the substrate were prepared by a combination of directional eutectoid decomposition followed by phase selective etching process. The thermal stability in the temperature range 500-700 degrees C of the obtained free standing and lying Au nanobelts were investigated in situ with a scanning electron microscope equipped with a high temperature stage. The results suggested that free standing Au nanobelts undergo morphological evolution in a different way compared with the substrate contacted lying Au nanobelts. The free standing Au nanobelts broke more easily and decayed into a chain of nanospheres following Rayleigh instability after the belt morphology changed into cylindrical wires; whereas the Au nanobelts lying on the substrate decayed into irregular particles. These findings clearly support a surface energy minimization driven mechanism. Only after transformation into a mainly {1 1 1} terminated structure formation of Rayleigh instabilities are observed. (C) 2012 Elsevier B.V. All rights reserved.