Abstract: MgS and TiS₂ were made at lab and the MgS-TiS₂（2%） disks were sintered at high temperature. A sulfur sensor using the MgS-based solid electrolyte was prepared and the galvanic cell can be expressed by Mo |SFe| MgS-TiS₂（2%） |Mo, MoS₂| Mo. The sulfur determination in liquid iron was carried out at 1375℃ without any protective atmosphere. The relation between the measured E and the chemical analysis %S can be shown as los%S=-0.3694-0.0077E（mV）（%S, 0.003-0.134）. Also,the determination of the sulfur potential of the (u-Cu₂S system shows that the partial electronic conduction parameter Pe’ is 6×10^-4 Pa for the MgS-TiS₂（2%） solid electrolyte at 1375℃.Pe’and fs were introduced for the correction of the E-%S relation.