High carbon ferro-manganese melt has been decarburized by blowing oxygen-argon mixture gas. Fraction of oxygen and flow rate of the gas mixture were changed to find out the optimum blowing schedule for the decarburization process. At initial blowing period, decarburization proceeds rapidly because of high carbon concentration. However, when carbon concentration decreases below about 2%, decarburization is degraded and simultaneously soidation of manganese occurs tremendously. An empirical equation has been proposed to analyze relationship between decarburization and oxidation of manganese in melt. Medium carbon ferro-manganese was made successfully by injection of oxygen-argon mixture without excessive oxidation of manganese.