The test equipment was newly made to observe chemical reaction characteristics between Na2O and iron based materials, and the reaction tests were carried out in argon gas at maximum temperature 1,473K. From the visual observation of the test and the X-ray analysis of the reaction products after the test, it was observed that the double oxides of Na-Fe and the sodium fume were generated from the results of the direct reaction ofNa2O and Fe. Using the thermodynamic database, it was expected that NasFeO4, which is stable in relatively high oxygen partial pressure, was generated at the first stage, and Na4FeO3, which is stable in relatively low oxygen partial pressure, was generated at the second stage. The reason of this variation of the double oxides of Na-Fe was considered that the oxygen concentration around the crucible was lowered by the sodium fume generated from the reaction at the first stage.