A novel gel hydrothermal oxidation route has been developed for preparation of nanocrystalline Co3O4 through the reaction between Co(OH)(2) gel and hydroperoxide in a hydrothermal system at 180 degreesC. X-ray powder diffraction (XRD) studies indicated that the product was well-crystallized cubic phase Of Co3O4 with a cell constant of a = 8.0722 Angstrom. The transmission electron micrograph (TEM) showed that the product consisted of monodispersive nanoparticles below 4 nm. (C) 2002 Elsevier Science B.V. All rights reserved.