Abstract: The effect of refining slag on inclusions was studied from two aspects, the activity of Al₂O₃ and the composition of inclusions. The activity of Al₂O₃ in a CaO-Al₂O₃-SiO₂-MgO(8%)-CaF₂ (8%) slag was calculated by the thermodynamic software Factsage, and the influence of slag basicity and (MgO) content on the activity of Al₂O₃ were analyzed. When the slag basicity increases from 1.0 to 2.0, the activity of Al₂O₃ in the slag decreases rapidly, and when the slag basicity increases from 2.0 to 3.8, the activity of Al₂O₃ has little change. There is little difference in the activity of Al₂O₃ between the slags with (MgO) mass fractions of 5% and 8%, and[Al]_s can be easily reduced into molten steel from the slag with high basicity. Many brittle inclusions containing MgO were found in wire rods with the high basicity refining slag, and by analysis the most appropriate basicity is 2.5 to 3.0.