Three-dimensional microstructures were fabricated and duplicated on copper and nickel substrates, respectively, using a confined etchant layer technique (CELT). The key feature of this technique is that the outer boundary of the diffusion layer of the etchant can retain the three-dimensional fine micro-pattern of the mold electrode. The etched patterns of copper and nickel were therefore approximately the negative copy of the gear-like three-dimensional mold and the duplication could reach a precision of (sub) gm. The design of an appropriate chemical etching system is one of the key issues to successful fabrication of microstructures on the bulk metal. The different processing parameters including the electrochemical current density and electrolyte concentration have strong influences on the smoothness of the fabricated surface. Our preliminary results demonstrate that CELT has the potential to be developed as an effective technique for micromachining three-dimensional metal microstructures, which can be applied for the fabrication of micro electromechanical systems. (c) 2004 Published by Elsevier B.V.