Abstract: The role of AlN on the internal oxidation behavior was investigated in Al-containing high Mn steels. Accelerated internal oxidation behavior was confirmed as Al contents increased. The sequential formation of internal oxidation and AlN + γ-matrix layers on the γ-matrix was observed in Al-containing steel after the heat-treatment in air. The former AlN + γ-matrix layer was replaced with the internal oxidation layer as the oxidation progressed. The heterogeneous nucleation of MnAl2O4 on the AlN was identified in between the internal oxidation and AlN + γ-matrix layers. MnAl2O4 shows the [1010]AlN//[112]MnAl2O4 and (0001)AlN//(111)MnAl2O4 orientation relationship with the pre-existing AlN by sharing Al atoms. The coherency between MnAl2O4 and AlN and the evolution of oxides in Al-containing high Mn steels were further discussed.