The anodic oxidation of Al 5083 and Al 6061 has been studied by steady state and transient polarization measurements in deoxygenated chloride solution containing sulphate ions at 22 degrees C. Complementary to the electrochemical studies, techniques such as scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were applied to investigate the morphological structure and chemical state of the electrode surface. The data suggests that a porous film of MgO and possibly Fe2O3 (for Al 6061) is formed on the electrode surface in addition to the aluminium oxide film (Al2O3). Some mechanisms for the growth of surface films on both alloys are discussed.