The reactions of copper on Au(111) electrode in the underpotential deposition (UPD) region from chloridemedia were investigated by cyclic voltammetry. Chloride concentrations ranged from trace levels up to0.55 M. At chloride concentration below 10-3 M three different adlayer structures were detected. At leastone of these structures also contains perchlorate ions besides copper and chloride. At NaCl concentrationsabove 5 × 10-3 M, Cu(I) is stabilized by chloride, and the reduction of copper proceeds as one electronprocess on the Au(111) surface covered with copper and chloride bilayer but not on Au(111) free of copper.