As part of the complete thermodynamic modeling of the Na2O-FeO-Fe2O3-Al2O3 system, the Na2O-FeO-Fe2O3-Al2O3 phase diagrams in air (1583 and 1698 K) and at Fe saturation (1573 and 1673 K) were investigated using the quenching method followed by Electron Probe Micro-Analyzer (EPMA) and X-ray Diffraction (XRD) phase analysis. General features of the phase diagrams in this system were well revealed for the first time. A complete meta-oxide solid solution between NaAlO2 and NaFeO2 was observed. An extensive solid solution of Na-2(Al,Fe)(12)O-19 Na-?-alumina was found and the existence of a miscibility gap in this solution was confirmed. Several compatibility triangles of three-phase assemblages were also identified in air and at Fe saturation.