The electrochemical behaviour of the copper-substituted Keggin-type and sandwich-type polyoxotungstate anions of the compounds α-[(C4H9)4N]4H[PW11CuIIO39] and α-B-[(C4H9)4N]7H3[CuII4(H2O)2(PW9O34)2] was studied by cyclic voltammetry in acetonitrile. In both cases two copper 1-electron reduction waves were detected in the cathodic scan. The first one was due to the reduction of one CuII to CuI in the polyoxoanion and the second one to the consecutive reduction of the preformed CuI to Cu0, with the consequent deposition/adsorption of the ejected metal atom at the glassy carbon electrode surface. In the anodic scan, Cu0 was re-oxidised with regeneration of the initial copper(II) complexes, via a CuI intermediate. The observed two-step reduction of copper(II) to copper(0) and the formation of intermediate species containing copper(I) is here reported for the first time for copper substituted polyoxotungstates. The co-ordination of the acetonitrile molecules to the copper ions must play a role in the formation of the copper(I) species, which are not detected in aqueous solution.