A novel method has been developed to prepare water-dispersible ethylenediamine (en)-stabilized ruthenium nanoparticles. The procedure involves the reduction of an en-RuCl3 complex by sodium borohydride. The Ru nanoparticles so prepared are fairly stable in water. TEM imaging shows a mean diameter of about 2.1 nm for the particles and a narrow particle size distribution. (C) 2003 Elsevier Inc. All rights reserved.