Abstract: The thermodynamic behavior of manganese and phosphorus between liquid iron and CaO-MgO-SiO₂-Al₂O₃-Fe_tO-MnO-P₂O₅ ladle slag system was addressed by investigating the thermodynamic equilibria between liquid iron containing Mn and P and the ladle slag at 1873 K. The Mn distribution ratio L_Mn increases with increasing Fe_tO content and decreasing the basicity ((%CaO + %MgO)/(%SiO₂ + %Al₂O₃ + %P₂O₅)) in slag, while the P distribution ratio L_p seems to be increased as Fe_tO content and the basicity increases. The values of L_Mn and L_p decrease by the addition of Al₂O₃ into slag. The expression of the dependence of L_Mn and L_p on the basicity and Fe_tO content in slag was obtained.