A method of producing ultralow phosphorus and carbon ferromanganese, comprising: preparing low carbon silicomanganese having phosphorus content of 0.03 wt% or less by charging low carbon silicomanganese comprising 55 to 60 wt% manganese, 25 to 30 wt% silicon, 0.04 wt% or less carbon and 0.08 to 0.1 wt% phosphorus with iron being a balance into a ladle furnace, supplying a stirring gas including argon or nitrogen while heating the low carbon silicomanganese to 1400 to 1650°C, thus making the low carbon silicomanganese homogeneous, adding the homogeneous low carbon silicomanganese with quicklime and fluorite and stirring them for 10 to 30 min, so that dephosphorization occurs to thus obtain 0.03 wt% or less phosphorus; preparing molten manganese slag composed mainly of high carbon ferromanganese slag by mixing 8 to 10% of manganese dust containing 66 wt% manganese, 8 to 13% of quicklime, 31 to 54% of high carbon ferromanganese slag containing 28 wt% manganese, and 30 to 53% of recycled high carbon ferromanganese slag containing 12 to 18% manganese in an electric furnace; subjecting the molten manganese slag and the low carbon silicomanganese having phosphorus content of 0.03 wt% or less to primary mixing and stirring at a ratio of 70-72: 28-30 in a ladle, thus producing a metal melt and slag; and subjecting the metal melt separated from the slag produced in the primary mixing and stirring and the molten manganese slag identical to that used in the primary mixing and stirring to secondary mixing and stirring, thus producing slag and a metal melt comprising 91-93 wt% manganese, 0.60-0.85 wt% silicon, 0.05-0.10 wt% carbon, and 0.015-0.02 wt% phosphorus. preparing low carbon silicomanganese having phosphorus content of 0.03 wt% or less by charging low carbon silicomanganese comprising 55 to 60 wt% manganese, 25 to 30 wt% silicon, 0.04 wt% or less carbon and 0.08 to 0.1 wt% phosphorus with iron being a balance into a ladle furnace, supplying a stirring gas including argon or nitrogen while heating the low carbon silicomanganese to 1400 to 1650°C, thus making the low carbon silicomanganese homogeneous, adding the homogeneous low carbon silicomanganese with quicklime and fluorite and stirring them for 10 to 30 min, so that dephosphorization occurs to thus obtain 0.03 wt% or less phosphorus; preparing molten manganese slag composed mainly of high carbon ferromanganese slag by mixing 8 to 10% of manganese dust containing 66 wt% manganese, 8 to 13% of quicklime, 31 to 54% of high carbon ferromanganese slag containing 28 wt% manganese, and 30 to 53% of recycled high carbon ferromanganese slag containing 12 to 18% manganese in an electric furnace; subjecting the molten manganese slag and the low carbon silicomanganese having phosphorus content of 0.03 wt% or less to primary mixing and stirring at a ratio of 70-72: 28-30 in a ladle, thus producing a metal melt and slag; and subjecting the metal melt separated from the slag produced in the primary mixing and stirring and the molten manganese slag identical to that used in the primary mixing and stirring to secondary mixing and stirring, thus producing slag and a metal melt comprising 91-93 wt% manganese, 0.60-0.85 wt% silicon, 0.05-0.10 wt% carbon, and 0.015-0.02 wt% phosphorus.