alpha-NaFeO2 is promising as minor-metal free cathode materials for low cost sodium-ion batteries. It has a flat voltage plateau at 3.3 V Vs. Na metal and a stable reversible capacity of 85 mAh g(-1) Fe3+/Fe4+ redox reaction on charge/discharge cycle was confirmed by Fe-57 Mossbauer spectrometer. The thermal stability of NaFeO2 cathodes with/without 1 mol dm(-3) NaClO4/EC-DMC electrolyte was investigated by DSC measurements. The fully-charged Na0.58FeO2 Powder decomposed thermally at a temperature higher than 300 degrees C, with Fe2O3 as a possible product. On the other hand, the mixture of Na0.58FeO2 powder and electrolyte showed exothermic heat in a temperature range of 220-300 degrees C. However, NaFeO2 showed better thermal stability in the electrolyte than LiCoO2 counterparts in Li ion battery systems, including less heat generation and higher exothermic onset temperature. This indicated that the Na-ion batteries might have comparable thermal stability with Li-ion batteries. (C) 2013 The Electrochemical Society.