Thin films of copper-indium-gallium mixed oxides/hydroxides are electrochemically deposited on molybdenum substrates in aqueous nitrate-based electrolyte in acidic conditions. The process is based on the local pH increase at the cathode surface due to the reduction of nitrate ions. A thermodynamical study shows that the electrochemically induced deposition of copper-indium-gallium mixed oxide/hydroxide films occurs at much higher potentials than their metallic counterparts. A voltammetric study presents the key role of Cu(II) reduction during the process to induce nitrate ions reduction, and shows that the deposition is then controlled by mass transfer of the Cu(II), In(III), Ga(III) species. The composition of the layer is remarkably precisely tuned in a large range of potential, which makes this process highly suitable for the synthesis of Cu(In,Ga)Se-2 solar cells. (C) 2014 The Electrochemical Society. All rights reserved.