We have fabricated porous aluminum oxide using flexible and thin aluminum foils with thickness of 0.025 and 0.2 mm. These foils were anodized with 0.3 M oxalic acid solution after being electropolished with ethanol/perchloric acid. During the anodization, the temperature of the electrolyte was maintained at $9^{circ}C$ and the anodization voltage was varied between 0.4 and 40 V The surface of the anodized aluminum oxide was studied with a scanning electron microscope. From the scanning electron micrograph, we observed that when the voltage applied was above 1 V for a long period of time, due to a strong electrolysis reaction in electrolyte, the surface of the anodized oxide was destroyed. However, when the anodization voltage was less than 1 V, the anodization process was very stable and lasted much longer. Our results show that for a thin aluminum foil, unlike a thick plate, one requires small anodization voltage less than 1 V to form a porous aluminum oxide for long anodization time.