The aim of our work was to characterise the oxide layers formed on a Cu-13Sn (mass%) alloy in a 0.5 M NaCl aqueous solution and to compare their properties to those obtained on pure copper and pure tin samples. Coulometric analyses allowed comparison of the thickness of the layers on the different materials, whereas impedance spectrometry provided information on the stability of the layers versus the immersion time. The photoelectrochemical method could be applied since both copper and tin oxides show semiconducting properties with well defined band gap values. On the Cu-13Sn alloy, Cu2O and SnO2 were simultaneously present at the surface, for short immersion times in the NaCl solution. This result was confirmed by XPS measurements. Nevertheless the predominance of the copper(I) oxide became clear after 48 h immersion. For comparison, similar measurements were performed and discussed in the presence of BTA, an inhibitor of the copper corrosion.