Abstract: The effect of top slag composition on MnO-Al₂O₃-SiO₂ inclusion composition was studied by controlling the condition of deoxidization and the composition of top slag in an experimental furnace in which the tire cord steel were melt. The Al₂O₃ content in the inclusion increased with the Al₂O₃ content of top slag increasing while the basicity of top slag was within 0.7-1.36. Plastic MnO-Al₂O₃-SiO₂ inclusion existed while the Al₂O₃ content of top slag was below 8%. The composition of MnO-Al₂O₃-SiO₂ inclusion can be controlled within the plastic area by controlling the condition of deoxidization and the composition of top slag.