The role of iron during anodizing of a non-equilibrium Al-4 atom % Fe alloy at high faradaic efficiency has been examined using high resolution transmission electron microscopy, Rutherford backscattering spectroscopy, and X-ray photoelectron spectroscopy. Anodic oxidation proceeds with initial formation of an anodic alumina film, free from iron species, and subsequent formation of an iron-contaminated alumina film, which is eventually contaminated by iron species throughout its thickness. During the initial oxidation of aluminum, iron atoms are accumulated in a thin layer of alloy, about 2-3 nm thick, immediately beneath the anodic film. When the average composition of the enriched alloy layer reaches approximately Al-25 atom % Fe, both aluminum and iron are oxidized and are incorporated into the film in their approximate alloy proportions in the presence of the enriched alloy layer. The incorporated iron species are in the trivalent state, and migrate outward in the growing anodic film about 1.8 times faster than Al3+ ions. The iron species eventually reach the film/electrolyte interface, forming a thin, iron-rich, hydrated layer probably composed of gamma-FeOOH.