This work describes preparation process of free-standing alumina membranes used in sensor devices for separation or purification (increased selectivity, and sensitivity) purposes. Nanoporous alumina membranes were prepared using anodic oxidation of aluminium foil in two types of acidic electrolytes and characterized using scanning electron microscopy. Membranes with pore diameters of 90 nm and 30 nm and thicknesses of 115 µm and 163 µm respectively were obtained. Fabrication of membranes with different post-treatment was also done. In this post-treatment process, etching of non-anodized aluminium and opening of barrier layer were replaced with application of reversible potential with equal magnitude as anodization voltage.