Cluster-support interaction in a Au-Fe3O4(0 0 1) system was studied using scanning tunneling microscopy, X-ray photoemission spectroscopy and Mossbauer spectroscopy, in situ, under ultra high vacuum conditions. Deposition of 0.02-5 monolayers of Au resulted in the growth of two-and three-dimensional gold nano-cluster. The positive shift of the Au 4f(7/2) electron binding energy for the smallest clusters was correlated with modification of the electronic structure in the surface magnetite layer, as found from Mossbauer analysis, leading to conclusion that a positive charging of small Au clusters can be responsible for their outstanding catalytic activity. (C) 2010 Elsevier B.V. All rights reserved.