Potential oscillations of a stainless steel electrode anodized galvanostatically have been observed in a mixture of chromic and sulfuric acids. The potential oscillated regularly between 1.6 V vs. SCE (lower) and 2.1 V (upper) with a certain frequency. The potential values were affected neither by the composition of chromic and sulfuric acids nor the magnitude of applied current density although the potential frequency was very sensitive to these parameters. This phenomenon is interpreted in terms of the repeated formation and disappearance of the saturated layer of dichromate ions on the electrode surface. Such a scheme is consistent with the in situ FTIR spectroscopic result that the concentration of Cr2O72- ions on the electrode surface increased with time during the polarization at the lower potential but the change in concentration of Cr2O72- ions was negligible at the higher potential.