Abstract: In the first part we have observed the electrotransport of molybdenum in carbonate media (OH–,CO=3) through a commercial electrodialysis anion exchange membrane. The values of the molybdenum, hydrogen oxide and carbonate fluxes obtained in this study show that molybdenum is present as molybdate ion MoO=4 in carbonate solution and that the molybdyl tricarbonate ion existence hypothesis MoO2(CO3)4–3 an't no longer be maintained. In order to confirm this result we have studied the electrotransport of molybdenum and carbonate ions with different CO=3/MoO=4 ratio. The used theory is based on the fact that, the concentration ratio in the membrane equals the one of the same species within the solution. These hypothesis have to be justified given that this equality is actually usual for unstirred layers extremity. Therefore, in the second part the concentration and the potential profiles in aqueous interfacial layers were determined by a numerical resolution of the Nernst-Planck electrodiffusion equation coupled with the Poisson equation. The obtained concentration profiles from numerical resolution differ from 3 to 6% from the ones acquired by analytical resolution method assuming the constant electrical field hypothesis for OH–, CO=3 ions, respectively. However the potential profiles display that constant electrical field hypothesis is strictly valid.