Abstract Dense alumina nanowire arrays were formed by a method that consists in a partial dissolution of the anodized aluminium oxide (AAO) membrane by chemical attack in 2 M H 3 PO 4 during 45 minutes, as a step immediately following the second anodizing. During this procedure the pore walls are partially dissolved by a controlled acid attack and the alumina nanowires arise as a consequence of this process, being the vertices of the hexagonal pores the origin of them. The thickness of them (≈40 nm) is slightly smaller than the diameter corresponding to the triple junction point of the membrane. By controlling the dissolution time it is possible to obtain alumina nanowires covering virtually the entire surface with lengths similar to the thickness of the AAO membrane that exceeding 10 μm. The steps of nanowires formation are discussed as follows.