Supercritical water was used as preparation media for particle deposited materials. Manganese oxide, silver, and lead oxide were prepared on alumina supports from metal acetate solutions in supercritical region. The resulting samples were characterized by X-ray diffraction (XRD), electron probe microanalyzer (EPMA), and transmission electron microscope (TEM). It is shown that metal or metal oxide particles could be crystallized onto the support surface, and could reach into the deeper part of the ball-type support with an increase of reaction time. It is also suggested that the crystallinity and composition of products can be controlled by temperature and pressure during the preparation with supercritical water. Analyses of the TEM images show the possibility to crystallize nano-sized particles. (C) 2004 Elsevier B.V. All rights reserved.