The effect of MgO and Fe_tO on the reoxidation and sulfide capacity of CaO-SiO₂ Al₂O₃ MgO_(sat)-Fe_t O( <10 wt% )slag system was investigated through the slag/metal equilibrium technique using MgO crucible at 1873 K for clean steel technology in ladle refining process. The MgO added into a slag to prevent the dissolution of refractory gives the high possibility to cause reoxidation of aluminum in liquid iron and deteriorates sulfide capacity of slag system. The CaO-SiO₂ Al₂O₃ MgO_(sat) slag system containing around 5 wt% Fe_tO is superior to that containing Fe_t O less than 2 wt% from the standpoint of both reoxidation of aluminum in liquid iron and sulfide capacity. The sulfide capacity as a function of slag composition could be obtained at 1873 K. logC_(S^(2-))=X_(CaO)-5.59X_(SiO₂)-5.30X_(Al₂O₃)+0.29X_(Mgo)+7.42X_(Fe₃O)-1.33.