Control over size and size distribution of nanoparticles has been the Subject of much interest during the past decade. In the present study, a simple strategy is described for obtaining monodisperse Pd nanoparticles with size less than 5 urn and size distribution around 10%. Without size-selective precipitation but with a simple reducing agent, hypophosphite, the synthesized Pd nanoparticles can form 2D well-ordered arrays on the TEM grids. When reducing agents were changed, no obvious size change of Pd nanoparticles was observed within experimental errors but the size distribution varied dramatically. In addition, stability, self-organized pattern, and solubility can be controlled by changing the capping agent. The present route is very simple and reproducible, and further study on the properties of the Pd nanoparticles is underway. (c) 2005 Elsevier Inc. All rights reserved.