The reducing dephosphorization of silicomanganese ferroalloys by CaO-based slags is investigated in the present paper. Experiments are carried out in an induction furnace in air atmosphere to simulate the practical production condition. It is found that dephosphorization took place very quickly by using CaO-CaF2 slag. In addition, decarburization and desulfurization also happened with the dephosphorization process. There is almost no dephosphorization when the silicon content in silicomanganese ferroalloy melt is less than 10 wt.%, while the dephosphorization ratio increases significantly as the silicon content is larger than 10 wt.%. When CaF2 in the slag is partly replaced by Al2O3, the dephosphorization ratio decreases sharply, and there is almost no dephosphorization for CaO-Al2O3 slag even when silicon content in the ferroalloy melt is 22 wt.%.