The protective films developed on copper by anodic polarization in a borate-buffered solution containing benzotriazole (BTAH), 1-hydroxybenzotriazole (BTAOH) or 3-amino 1, 2, 4-triazole (ATA) have been characterized using coulometric experiments and an electrochemical quartz crystal microbalance (EQCM). The combination of these two techniques has allowed the CuO and Cu2O layers and the cuprous–organic layer to be analyzed quantitatively. In the presence of BTAOH, the oxide layers were very similar to those formed in inhibitor-free solution and BTAOH appeared to be adsorbed on the oxide film. In the presence of BTAH, a thick Cu2O film was covered by a Cu–BTA film containing 8% Cu+ ions. Cupric oxide appeared on Cu2O areas uncovered by Cu–BTA. In the presence of ATA, the Cu2O layer was very thin and the greater part of Cu+ ions (75%) was involved in a thick Cu–ATA film.