The MnO–SiO₂-type inclusions changed into MnO–Cr₂O₃ type inclusions in an Fe–Cr alloy deoxidised by Mn and Si with a low Si concentration by heat treatment at 1473 K. At high Si content, the MnO–SiO₂-type inclusion remained stable even after heat treatment. The change in the chemical composition of the oxide inclusions by heat treatment depended on the concentrations of Si and Cr in the Fe–Cr alloys. The mechanism of the change in the chemical composition of the oxide inclusions was investigated by using two experimental methods. The solubility of Cr₂O₃ in MnO–SiO₂ was measured from 1473 to 1673 K. The solubility of Cr₂O₃ decreased with temperature. The other experiment was performed using a diffusion couple method between the Fe–Cr alloy and MnO–SiO₂ at 1473 K to investigate a reaction between them. The formation of MnO–Cr₂O₃ was observed at the interface. It is found that both the decrease in solubility of Cr₂O₃ and diffusion of Mn, Cr, and Si at the interface between the Fe–Cr alloy and oxide inclusions are important for controlling the change in the chemical composition of the oxide inclusions in the Fe–Cr alloy by heat treatment at 1473 K.