Abstract: The effect of top slag composition on CaO-Al₂O₃-SiO₂ inclusion composition was studied by controlling the condition of deoxidization and composition of top slag in experimental furnace in which the tire cord steel was melt. The content of Al₂O₃ in inclusion increased with that in top slag increasing while the basicity of top slag was fixed. Plastic inclusion presented while the content of Al₂O₃ in top slag was below 8%. It is concluded that the composition of the inclusion can be controlled within the plastic area by controlling the condition of deoxidization and the composition of top slag.