A wet powder spraying (WPS) method was applied to prepare protective layers of manganese cobalt spinel oxide (MCO) on commercial stainless steels of solid oxide fuel cell (SOFC) interconnects. Densification of the MCO layer was dependent on the thermal treatment condition in which a reactive sintering increased the coating density. An applied MnO sublayer reacted with the MCO layer during sintering, and resulted in secondary phase formation and limited densification. Both MCO and MnOMCO coatings were adhering to the steel substrates and suppressed chromium diffusion during oxidation. The area specific resistance (ASR) of a test specimen including the MCO layer was 0.03 Ωcm2 at 700°C after 800 h, lower than with MnO-MCO, which is believed to be due to the denser protective layer of the single phase and more limited chromia scale growth. Thus, an effective protective layer of metallic interconnects could be prepared using a simple wet coating method after optimization of the sintering conditions.