Polarization and impedance measurements were performed on aluminum in 0.1, l and 3 mol/l NaOH. The frequency range studied was 1×10 −2–1×10 4 Hz in the potential range −2 to −1 V vs. SCE. In polarization experiments the potential was extended up to 0 V vs. SCE. The behavior of the system was characterized by a high frequency capacitive loop related to the charge transfer due to dissolution of the metal, an inductive loop at medium frequency which we have attributed to surface roughening and a second capacitive loop obtained at low frequency which has been ascribed to the adjustment of the surface film to the change in potential resulting in higher charge transfer resistance.