Porous anodic alumina thin films with structural colors were fabricated in phosphoric acid electrolyte using a one-step electrochemical oxidation of aluminum. The films displayed uniform structural colors and radially symmetric rainbowrings of structural colors at different experimental conditions. The microstructures indicated that the thickness of the films diminished symmetrically outward from the center of the films. The experiment indicates that the role of cathode carbon rod is similar to a small sphere electrode in the process of electrochemical reaction. A theoretical study of the anodization in alumina films with these rainbow rings is consistent with the experimental results. The present results contribute to understanding the anodization mechanism of many porous anodic oxides. (C) 2016 Elsevier B.V. All rights reserved.