We have carried out a systematic investigation of the anodization procedure in order to determine the exact chemical mechanism of the dissolution process responsible for pore formation in nanoporous alumina templates. We measured the anodization current as a function of time and compared it with the thickness of porous aluminum oxide layer obtained from cross-section scanning electron microscopy images. From this, we calculated the number of moles of electrons generated per mole of porous alumina grown. This analysis is consistent with a reaction mechanism in which aluminum is converted to aluminum oxide in addition with the direct transfer of aluminum ions across the thin barrier aluminum oxide into the electrolyte. Hence, experimental evidence is reported that indicate that the dissolution process observed is that of Al3+ ions migrating across the barrier layer and dissolving into the solution. Contrary to the suggestion of some authors, these experiments indicate that at most a negligible amount of oxide dissolves during the anodization of aluminum. (c) 2006 The Electrochemical Society.