Thin films of porous anodic aluminum oxide have been prepared on an electrically insulating support by the anodization of aluminum films sputtered onto glass slides. The resulting transparent aluminum oxide films were characterized by scanning electron microscopy and variable angle ellipsometry. Subsequently, the film was modeled from the ellipsometric data taken. An underlying conductive medium is not necessarily needed to bring about nearly complete anodization of the aluminum layer. (C) 2003 The Electrochemical Society.