Effects of cerium (Ce) on the microstructure and corrosion resistance of high manganese steel (HMS) in 3.5 wt % NaCl were investigated. It was found that the carbides in the grain boundaries in HMS were refined with the addition of Ce. The corrosion current density was reduced to about one-fifth of the original with the addition of Ce, and the resistance of the oxide film (R_f) with the addition of Ce was 2.549 × 10³ Ω cm^–2, which was increased by nearly an order of magnitude compared with that of without Ce addition. When Ce was added, the degree of segregation of carbides in the HMS substrate was weakened, and the entire corrosion process was dominated by uniform corrosion. The corrosion product film of HMS with the addition of Ce was relatively dense and uniform. The corrosion resistance of HMS with the addition of Ce was improved significantly. The influence mechanisms of Ce on the microstructure and corrosion resistance of HMS are also discussed.