Corrosion processes occurring on copper in borate solutions were studied using electrochemical dc and ac as well as surface analytical techniques. It was found that at pH 7 in the absence of sodium dodecylsulfate (SDS), passivity occurs through the formation of a duplex Cu2O/CuO, Cu(OH)2 structure. In the presence of SDS, passivity breakdown is attributed to formation of the Cu(DS)2 complex which has also been detected by reflectance Fourier transform infrared spectroscopy. AC impedance spectroscopy implies that migration of copper ions within the oxide film to the oxide surface proceeds more readily in the presence of DS- at the potential where passivity breakdown starts to occur (0.050 V vs. SCE). At pH 7.5 no passivity breakdown is observed due to oxidation of Cu2O to CuO rather than to Cu2+.