Abstract: The variations of the total oxygen content, the amount, size and morphology of inclusions in three heats 0. 6% C steels were studied systematically by sampling of molten steel and slag during LF refining and continuous casting. The results show that the total oxygen content of three heats 0. 6% C steel is about 0.007 0% in start of LF refining, the total oxygen content of three heats 0.6% C steel is reduced slowly and the total oxygen content in the casting blank is reduced to less than 0. 003% during start of LF refining→ after calcium treatment→end of soft argon stirring→ tundish casting→ casting slab. In start of LF refining, the inclusions of three heats 0. 6% C steel are mainly SiO₂-MnO-(Al₂0₃ ) inclusions, which are the deoxidized products of silicon and manganese. After calcium treatment, the inclusions in the steel are transformed into CaO-SiO2 -Al₂O₃ -MgO whose main components are CaO + MgO 20% ~40% , SiO2 20% ~40% , Al₂O₃ 30% ~50%. Due to the secondary oxidation of molten steel during tundish pouring, the total oxygen content of molten steel and the a¬mount of SiO₂-MnO-( Al₂O₃) of the secondary oxidation products in 0. 6% C steel tundish have increased significantly.