In the current investigation, the thin film method was employed to clarify the formation mechanism of the oxide layers at the interface between the Al₂O₃–SiO₂–C refractory and liquid Fe. A reacted layer was formed in such a way that initially FeO-enriched liquid layers are widely distributed on the Fe surface and FeO and SiO₂ in the liquid layer are reduced by Al in liquid Fe to develop solid Al₂O₃-enriched layer of inclusions. Some inclusions in liquid Fe might be produced by the remaining oxygen in Ar gas being supplied through the nozzle to prevent the adherence of inclusions onto it. The oxide layers at the interface estimated by thermodynamic calculation are in good accordance with the experimental results of the reaction between Al₂O₃–SiO₂–C refractory and Al-killed/Al-Ti-killed steels previously reported.