Inhibition of copper in a desearated sodium heptanoate solution (0.08 M, pH 8.0) by electro-oxidation has been investigated. R-p measurements were carried out to compare inhibition efficiency using this original method with that based on other usual chemical oxidation methods. In-situ spectroscopic and kinetic ellipsometric measurements have been performed to study the passivation mechanism of copper. The inhibition of copper is attributed to the formation of a protective layer composed of a mixture of copper II heptanoate and copper hydroxide. Two growth rates are observed during the passivation process. A model of a duplex layer is proposed. The thickness of the passive film is evaluated at 14 +/- 1.5 nm.