Using 65Zn and 35S marked zinc sulphate, we have shown with a zinc rotating disk electrode, that in saturated solution of zinc sulphate, after formation of a pore-free salt layer, the anodic reaction consists in the direct reaction of the metal with sulphate ion into solid salt. We determined the rate of exchange of zinc and sulphate ions between the saturated solution and the salt. From the cd after formation of the pore-free passive layer, and from resistance measurements, we deduce that above a very thin layer of anhydrous zinc sulphate there exists a layer of ZnSO 4.7H 2O, which is 0.6 to 1 × 10 4 times thicker. The specific resistance of the anhydrous salt at 25°C is ϱ w = (2.4 ± 1.5) × 10 11 Ω.cm and that of the ZnSO 4.7H 2O layer ϱ l = (4.0 ± 1.1) × 10 6 Ω.cm.