Disclosed is a method of producing ultra low phosphorus and carbon ferromanganese having 0.1 wt % or less carbon and 0.03 wt % or less phosphorus. The method includes preparing low carbon silicomanganese having low phosphorus content, preparing molten manganese slag, subjecting the molten manganese slag and the low carbon silicomanganese having low phosphorus content 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 above slag 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 including 91˜93 wt % manganese, 0.60˜0.85 wt % silicon, 0.05˜0.10 wt % carbon and 0.015˜0.02 wt % phosphorus.