<p>The effect of Al₂O₃/SiO₂ molar ratios on the structure and crystallization behavior of CaO–SiO₂–Al₂O₃–MgO–CaF₂ oxide melts representing the slag inclusions in stainless steel was studied. The results show that the degree of polymerization of the oxide melts decreases as the Al₂O₃/SiO₂ molar ratios increase. The relative proportion of silicate network structure units decreases as Al₂O₃/SiO₂ molar ratios increasing, whereas the relative fraction of aluminate network structure units increases. The temperature of crystallization of the oxide melts decreases as Al₂O₃/SiO₂ molar ratio is increased, and the undercooling for starting crystallization increases from 48 K (48 °C) to 233 K (233 °C), which indicates a reduced crystallization ability of the oxide melts. Ca₁₂Al₁₄F₂O₃₂, MgO·Al₂O₃, Ca₂SiO₄, and MgO crystalline phases precipitate sequentially in the process of continuously cooling of oxide melts, except the absence of MgO in the melts with Al₂O₃/SiO₂ molar ratio of 0.61 and MgO·Al₂O₃ spinel in the melts with Al₂O₃/SiO₂ molar ratio of 1.69. The size and amount of MgO·Al₂O₃ spinel and Ca₂SiO₄ crystalline phases decrease as Al₂O₃/SiO₂ molar ratios increasing. The size and amount of Ca₁₂Al₁₄F₂O₃₂ and MgO crystalline phases increase as the molar ratios of Al₂O₃/SiO₂ increase.</p>