We have studied pore nucleation and growth of anodic porous alumina with square cells in the initial stage of anodizing by measuring current density transient at constant voltage and by observation of film structure at different stages. The initiation sites of pores were laid out in square lattice patterns using imprinting process. The obtained oxide film was formed by a close-packed array of square cells following the imprinting pattern. The shape of the pore was circular at the surface, but square at the bottom of the film corresponding to the shape of square cell at the steady-state growth stage. At the same time, crystalline particles located at fourfold point of cells were detected. The surface of Substrate after removal of oxide film revealed that the crystals were regularly ordered aluminum pillars placed at every fourfold point of cell junction. From these characteristic structures, it is concluded that the unusual arrangement of initiation sites, which is different from ordinary hexagonal cell arrangement, could control the growth of anodic porous alumina significantly. (C) 2003 Elsevier Science Ltd. All rights reserved.