The time-potential curves of manganese electrodes in oxygenated solutions of PO43-, HPO42- and H2PO4- anion of different concentrations are constructed. Also the critical current densities for passivation of Mn electrodes are determined. Both indicate that promotion or inhibition of the corrosion of Mn depends on the type and concentration of the phosphate ions. The plots of log ip as a function of log C for HPO42- and H2PO4- satisfy the relation log ip=A+B log C, whereas that of PO43- anion is according to the relation log ip=A-B log C; (A) depends on he type of the anion in solution.