In this study, the corrosion behavior of Mn-Co metallic coating on SUS430 steel in reducing atmosphere is evaluated at 800 °C. Samples are coated by commercial physical vapor deposition (PVD) and oxidized in humidified H2/N2 for 1250 hours. The results show the instability of this Mn-Co metallic coating in reducing atmosphere and the failure to protect the base material. Further investigation by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy proves that the desired Mn-Co spinel cannot be formed in reducing atmosphere. In conclusion, this Mn-Co coating is not appropriate for the protection of corrosion of SUS430 interconnect at anode side. New materials need to be found for good protection of the steels in order to increase the long-term performance of fuel cell stacks.