A high alumina refractory, glazed by typical ladle slag of CaO–MgO–Al₂O₃–SiO₂ was investigated to understand the influence of the glazed refractory on the generation of non-metallic inclusions in Al-deoxidized molten steel at 1600°C. The variations of microstructure and chemistry of the glazed refractory with reaction time were studied. Thermodynamic analysis was simultaneously carried out to understand the complex chemical reactions. During the reaction between the glazed refractory and molten steel, two chemical reactions were observed: between glaze and molten steel, and between glaze and original refractory. By the chemical reactions, SiO₂ in the glaze was reduced to [Si] by [Al] in molten steel. The glaze layer also gradually changed from the liquid CaO–MgO–Al₂O₃–SiO₂ phase with small amount of embedded spinel particles to the liquid CaO–MgO–Al₂O₃ phase with embedded spinel and CaAl₄O₇ particles. Severe erosion was observed in the porous spinel area of a refractory. Spinel inclusions were found as major inclusions originated from the glazed refractory. The erosion mechanism of the glazed refractory was proposed in the present study.