Self-ordering of the cell arrangement of the porous structure of anodic alumina has been studied in a sulfuric acid solution. Ordering of the cell arrangement was dependent on the applied potential, and a highly ordered structure was obtained under anodization at a constant potential of 25 to 27 V. Self-ordering of the porous structure proceeded with the growth of the oxide layer under anodization at an appropriate potential, and a porous film with an almost ideal hexagonal honeycomb structure was formed over an area of several micrometers after a long period of anodization.