The behavior of cuprous species at electrodes polarized in hydrochloric acid solutions has been investigated in order to obtain the fundamental knowledge of electrodeposition of copper from chloride media. The rest potentials of the cuprous/copper couple in hydrochloric acid solutions were determined by the activity of the Cu+ aquo cuprous ions. It was found that the rest potential could be controlled by the concentration of chloride ions according to their correlation with the aquo species. Dissolution of metallic copper primarily yielded Cu(I) species in hydrochloric acid solutions, in contrast to the Cu(II) species in sulfuric acid solutions. However, cuprous chloride precipitation may also appear in 1-2 mol dm(-3) hydrochloric acid solutions and even cuprous oxide may be formed at the surface of the copper electrode at higher HCl concentrations. The experimental results suggested the possibility to produce a relatively dense and smooth deposited surface, while reducing the power consumption of copper electrowinning. [GRAPHICS] .