The effects of I- adsorption on the electrodeposition (under and overpotential deposition) of Cu on polycrystalline Pd electrodes were studied in dilute perchloric acid solutions at 18 degrees C. It had been found that Cu underpotential deposition on polycrystalline Pd exhibits different potentiodynamic features, which are characteristic of defined crystallographic planes of Pd. However, these features varied when the voltammograms were performed in the presence of strongly adsorbable anions, such as I-. In spite of having found a partial inhibition of the Cu voltammetric features in the presence of I-, we calculated integer numbers in the electron transfer to Cu2+ and I- ions. The change in the values of Cu massive deposition potential due to the presence of I-was caused by the appearence of a new electrode, that is, the Cu/CuI/I- interface.