A technique for optimization of steel chemistry for MnS precipitation on oxide inclusions has been developed through employing the computational thermodynamic method. The optimum composition of Si/Mn deoxidized steel was estimated to be Fe-0.1mass%C-0.1mass%Si-1.5mass%Mn-0.01mass%O-0.007mass%S. The prediction was validated by experiments using a semi-levitation melting technique. The inclusions mainly consisted of MnO-SiO₂ oxides with MnS precipitates. The observed morphology revealed a possibility of both oxide and sulfide having been precipitated as liquid phase, although the existing thermodynamic data do not support this to occur.