The electrochemical reduction of metal oxides provides an appropriate technique for the production of nanocrystalline mesoporous metals at room-temperature. Polycrystalline sintered CuO and Cu2O single crystals were reduced to Cu in this study. Electron microscopy and diffraction results demonstrate the dependence of the metal microstructure on the preparation and post-treatment conditions. The size and microstrain of the crystallites are controlled mainly by the preparation temperature. This method enables the reproducible production of medium-scale nanocrystalline metals independent on critical process parameters.