We prepared a set of nearly monodisperse gold clusters ranging from 1.3 to 10 nm by a seed-mediated growth in the presence of poly(N-vinyl-2-pyrrolidone) (PVP). The seed clusters with a diameter of 1.3 +/- 0.3 mn were prepared by reducing AuCl4- with NaBH4 in a low-temperature aqueous solution of PVP. Subsequent reduction of more AuCl4- by Na2SO3 in the presence of the seed clusters yielded a series of larger Au:PVP clusters. Catalytic activities of the Au:PVP clusters for aerobic oxidation of p-hydroxybenzyl alcohol increased with decrease in the core size. The size dependence is discussed in light of the electronic structures of the cores probed by optical spectroscopy. (c) 2006 Elsevier B.V. All rights reserved.