The metal oxides formed at the surface of brass (90Cu10Zn) foils exposed to a low-pressure inductively coupled oxygen plasma were identified by linear sweep voltammetry and X-ray diffraction spectroscopy. The plasma treatment confirms the formation of copper and zinc oxides (i.e., Cu2O, CuO, and ZnO). The electrochemical reduction curves in aqueous solutions of the different brass samples show that ZnO oxide is reduced after all the copper oxides. The reduction potentials of copper and zinc oxides vary with the thickness of the oxide layer and decrease as the exposure time to the plasma at a fixed energy density increases. A mechanism is proposed for the reduction of thin films containing the Cu2O, CuO, and ZnO oxides formed at the surface of the samples.