A simple electrolysis process employing plain water as an electrolyte was used to prepare Cu(OH)(2), CuO, Cu2O nanostructures with different morphologies. No special electrolytes, chemicals, and surfactants are needed. In addition, the FeOOH, Fe3O4, ZnO, and Ni(OH)(2) nanostructures were also synthesized by this route, indicative of the universality of the solution route presented herein. The morphologies and structures of the obtained nanostructures have been characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), power X-ray diffraction (XRD), and UV-vis absorption spectra. Furthermore, the mechanism for the formation of metal hydroxide and oxide nanostructures has been preliminarily discussed. The successful preparation of metal-based nanostructures under mild conditions could be of interest for both applications and fundamental studies. (C) 2007 Published by Elsevier B.V.