This paper describes a one-step magnetron sputtering technique for the preparation of supported catalyst particles that has a number of advantages over existing methods. In order to demonstrate the effectiveness of this technique, a supported gold on gamma-Al2O3 oxidation catalyst has been prepared. This catalyst is as active as catalysts prepared via traditional chemical methods for the oxidation of carbon monoxide (TOF 1.1 conversions/surface Au atom/second at 300 K and 16% CO/8% O-2/He). Aberration-corrected scanning transmission electron microscopy demonstrates that this technique produces gold nanoparticles in a size range that is claimed in the literature to be most active (about 2 nm). (c) 2004 Elsevier Inc. All rights reserved.