It is very important in copper smelting and refining processes to remove minor elements such as lead, bismuth, etc. LS-Nikko Copper has employing two major processes: Outokumpu process and Mitsubishi continuous process. In converting stage, Pb content in blister copper produced from Mitsubishi process using the CaO-FeOx-Cu2O slag is higher than that from Outokumpu process which accepting the FeO-SiO2 slag. Therefore, it is needed to investigate the Pb removal method from blister in the fire refining stage in Mitsubishi process. In the Mitsubishi process, silica sand and process slag are generally mixed as a potential flux to remove Pb from blister. However, the effect of CaO and Al2O3, which are also contained in process slag, on the distribution ratio of Pb between slag and blister is still unknown. Therefore, in the present study, the distribution behavior of lead between molten Cu and FetO-SiO2(-Al2O3,CaO) slags was investigated in view of thermodynamics.