The surface diffusion energy of Au on the root 3 x root 3 Au-Si(111) reconstructed surface is determined from low energy electron microscopy experiments. We have used two methods, one based on the nucleation of Au particles, the other one on the island growth by Ostwald ripening. The two methods give E-d = 1.10 +/- 0.34 eV and E-d = 1.56 +/- 0.31 eV respectively and with a weighted mean we obtain E-d = 1.3 +/- 0.2 eV. We suggest that this high activation energy could be due to a mechanism of diffusion by exchange. (C) 2015 Elsevier B.V. All rights reserved.