In this study, BaFeO4 was prepared from K2FeO4 and characterized by SEM, XRD, IR, and TG. BaFeO4 is insoluble in pure water and it solubility increases with the increase in the concentration of KOH solution. The measured solubility of BaFeO4 is higher than that of K2FeO4 in saturated KOH solution at 25 degreesC, and may be due to the presence of a higher concentration of carbonate in the concentrated KOH solution. BaFeO4 has been found to decompose both in dry environment and in KOH solution. The instability of BaFeO4 is studied in detail by mean 3 of constant current discharge, XPS, XRD, and IR spectra. The reason why BaFeO4 is not stable is discussed in this paper. (C) 2004 Elsevier Ltd. All rights reserved.