Low-temperature-sintered MnCo2O4–MnO2 coatings have been prepared on pre-oxidized SUS430 ferritic alloy by slurry coating. The effect of pre-oxidation treatment before slurry coating is then investigated. Microstructural and electrical characterizations show that 25 h of pre-oxidation at 800 °C could significantly improve the oxidation resistance of the coated alloy and effectively inhibit the increase in area-specific electrical resistance during long-term oxidation. These effects can be explained by the interfacial reactions between the coating and the pre-oxidized alloy during sintering and oxidation tests. Furthermore, this study suggests that the dense reaction layer at the coating-alloy interface could be the key to improving the oxidation resistance of metallic interconnects with low-temperature-sintered spinel coatings.