The anodic oxidation of zinc and zinc ‐tin alloys at very low current density was carried out in solutions of different pH values using the direct potentiometric method. In the case of zinc, the primary oxidation product was a film of zinc oxide or hydroxide less than one molecule thick. When tin was alloyed in different concentrations with zinc, the anodic process resulted in the successive formation of zinc hydroxide, stannous and stannic hydroxides before oxygen evolution. The alloys required less quantities of electricity to passivate than their pure components, thus revealing their noble character. The passivation of the alloys in 0.1N nitric acid is due to a chemical and not to electrochemical process. Critical current densities for passivation also revealed the noble character of the alloys.