The electrotransport of Cr(VI) oxo anions through an anion exchange membrane (AEM) is investigated as functions of the CrO3 concentration and pH on both sides of the membrane. This transport strongly depends on the polychromate ion formation within the membrane, which is favoured by both the very high concentration compared to that of the bulk solution and the proton leakage usually encountered when an AEM is in contact with acid solutions. Their formation is closely connected to the pH of the donor compartment of the electrodialysis cell. Their presence can lead to an inversion of the AEM permselectivity. The increase of the transport number of Cr(VI) species is associated with the reduction of the proton leakage.