In order to investigate the dependence of the sputtering yield on cluster size, surfaces were irradiated with cluster ion beams with various size distributions, and the sputtering yields were measured. It was found that there was a threshold energy for sputtering with cluster ion irradiation. When the cluster size was constant, the sputtering yield was proportional to acceleration energy. These results suggested an empirical formula to calculate sputtering yield from the ion energy and the size distribution of the cluster. The empirical formula indicates that the sputtering yield is proportional to the 1.1 power of the size, when the acceleration energy per atom is constant. (c) 2005 Elsevier B.V. All rights reserved.