The anodic dissolution of aluminium in organic AlCl3/dimethylsulfone electrolytes was investigated by measuring anodic potentiostatic polarization curves and AC impedance responses on a rotating disc electrode. Mass transport limited current plateaux are obtained. They are related to the limitation of the dissolution rate by the diffusion of Al3+. The variations of the ac impedance responses with rotation rate and applied potential are interpreted with models that assume the presence at the surface, of an aluminium chloride salt layer. The salt layer has a duplex structure composed of an inner compact layer through which aluminium ions migrate by high-field conduction and an outer porous layer where ionic conduction occurs in the electrolyte filling the pores.