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 Na2(Al,Fe)12O19 Na-βˮ-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.