We have proposed a novel process for recycling Mn wasted in steelmaking slag via sulfurization to separate P from Mn. For clarifying the efficient recovery of Mn from steelmaking slag, the influences of slag basicity and temperature on the distributions of Mn and Fe between the Fe-Mn-Ca-O-S matte and FeO- MnO-MgO-P2O5-SiO2-CaO slag were investigated. The distributions of Fe and Mn between the matte and the slag increased with an increase in the slag basicity. Moreover, when log P S2 (PS2: partial pressure of S) was more than ?2, the Mn distribution increased to be more than 10 as the slag basicity increased beyond 1.7. Even though the effects of slag basicity and PS2 on the Mn content in the matte were small, the behavior of Mn in the matte was dependent on temperature. In order to understand the behavior of Mn and Fe in steelmaking slag and matte, the relationship between the activity coefficient ratio of MnS and FeS (λMnS/λ FeS) and the mole fraction ratio of MnS and FeS for the matte was investigated. To evaluate λMnS/λ FeS for the matte, the activity coefficient ratio of MnO and FeO (λMnO/λ FeO) was estimated using an empirical formula and the RS model, and the mole fractions of MnS and FeS in the matte were calculated on the basis of mass balance. The results revealed that the values of λ MnS/λ FeS for the Fe-Mn-S-O matte were about twice those for the Fe-Mn-Ca-S-O matte. Moreover, λMnS/λ FeS for the Fe-Mn-Ca-S-O matte decreased with an increase in temperature.