Abstract: A solid state galvanic cell has been employed to determine the phase diagram of the ternary system Li-Fe-S in the temperature range from 360 to 550℃. Li₄SiO₄ +40m/o Li₃PO₄ was used as an electrolyte. According to the general principle to investigate the phase diagram with electrochemical coulometrio titration, the samples do not have to be quenched and only electrical quantities are required to be measured. Thus, the partial phase diagram of ternary system Li-Fe-S for the region of lithium content lower than 10 atom% and Fe:S atomic ratio bigger than 47:53 has precisely been constructed.