Hybrid composites of US nanoparticles embedded in epoxy resin matrixes have been prepared by co-precipitate method and characterized. Epoxy resin acted as the matrix for the formation of nano US particles in the reaction system and kept them from agglomerating. The resulting viscous orange liquid could be cured with normal curing agent. The result of XRD, UV and TEM analysis reveals that the US particles are in nano size and dispersed in epoxy resin matrix homogeneously. (C) 2003 Published by Elsevier Ltd.