The effect of different amounts (0.35, 0.85, and 1.20 kg per tonne) of misch metal addition to three ingots of electric arc melted 20MnCr5 grade case-carburizing steel was examined. A minimum amount of REM is necessary to avoid an increased inclusion population which originates because of poor floatability of RE (Ca, Al, Mn) oxides formed with smaller additions. The cleanliness improves with increasing REM addition and formation of RE Sulfides and oxysulfides. The mechanical properties studied reflect the inclusion characteristics of the ingots. The hot ductility, room-temperature tensile and impact properties, and fatigue resistance of the steel respond in different manners to changes in inclusion parameters such as size, shape, distribution, and composition.