This communication studies the CO 2 reduction reaction in H 2 O/CH 3 CN mixtures on nanostructured copper. It was found that nanostructured copper electrode presents a welldefined voltammogram in acetonitrile, where it can be seen three signals related to adsorbed or surface attached (thin films) species. Also, it was found that the current density of CO 2 reduction in mixtures H 2 O/CH 3 CN on nanostructured copper electrodes with a molar fraction around 0.25 is higher than those observed with molar fractions lower than 0.15 or higher than 0.35. Finally, nanostructured Cu electrodes show higher catalytic activity towards the CO 2 reduction than copper electrode.