Abstract: A technique for treating 16 Mn steel with high-La mischmetal additives was proposed. The effect of the additives on the inclusion and mechanical properties of 16Mn steel was investigated and compared with that of Ce-rich additives. It is shown that high-La rare earth additives play a role in modifying inclusion and improving properties of the steel. The optimum effect of RE occurs when the mass ratio of RE/S=2.5. The high-La mischmetal can replace Ce-rich mischmetal with RE additives for treating 16 Mn steel.