Abstract: There are abundant manganese mineral resources in Chengkou and Xiushang County, Chongqing City, as well as a phosphorus content that is over the national standard; thus, the mass percent of phosphorous in Si-Mn alloys produced from manganese ores is over 1%. This can easily result in "cold brittleness" and reduce the steel quality when the alloys are used for deoxidation and alloying in steelmaking. Therefore, it is important to research on the dephosphorization of Si-Mn alloy. Dephosphorization of a high-phosphorus Si-Mn alloy was studied under dephosphorizing agents of Si-Ca alloy, rare earth silicon, and Al-based dephosphorizer in a silicon molybdenum furnace of 1400℃. In the experiment, CaO-CaF₂ (mass ratio of 25:75) was used as a covering slag, and the ratio of slag-metal is 0.2:1. The phosphorous content in the Si-Mn alloy after dephosphorizatoin was detected by an inductively coupled plasma (ICP) spectrometer, and the phase composition of the slag was analyzed by X-ray diffractometry (XRD). The effects of different dephosphorizing agents and their dephosphorization rates were analyzed. The results show that the dephosphorization rate increases with dephosphorizer content. For Al-based dephosphorizer, the dephosphorization effect is optimum at 8% dephosphorizer content, whereby the phosphorus content in the Si-Mn alloy is reduced to 0.21%, which meets the national standard (≤ 0.25%), and the dephosphorization rate reaches 78%. The efficiency of Si-Ca alloy is lower; the dephosphorization rate is 47% even when the alloy content reaches 10%. The effect of rare earth silicon is the least; the dephosphorization rate is 22% when the content reaches 10%. Thus, the Al-based dephosphorizer is the best dephosphorization agent under the present experimental conditions.