The present work deals with a study of the phase relationships in the system Fe-Na-O in the temperature range 500 to 1400 ‡C. DTA measurements were combined with X-ray diffraction and high-temperature microscopic methods to investigate phase transitions involved in the system. The oxygen partial pressures in equilibrium with the Na₂O-Fe_xO solid solutions were measured by means of the galvanic cell (-) Fe,Na_yFe_zO||ZrO₂-CaO||Fe_xO,Fe (+) in the temperature range 760 to 910 ‡C. From the results obtained in the present work, the phase diagrams of the systems FeO-Na₂O, Fe3O4-Na₂Fe₂O₄, FeO-Na₂Fe₂O₄ have been constructed. The liquidus projections in the system FeO-Fe₂O₃-Na₂Fe₂O₄ and an isothermal section of the ternary system Fe-Na-O at 595 ‡C have also been presented.