The oxidation of pure iron and iron-aluminum alloys coated with Na 2SO 4 in O 2—;0.5–1.0% ( SO 2 + SO 3) at 650–700°C was studied by employing thermogravimetry, metallography, X-ray diffractometry, SEM and electron microprobe analysis, and chemical analysis. It was found that Na 2SO 4 deposits markedly accelerated the oxidation of pure iron and Fe-Al alloys in these conditions. The accelerated oxidation was associated with the formation of a eutectic melt of Na 2SO 4-sulfates of iron. With pure iron, direct growth of oxides on the metal surface predominated, though fluxing contributed a little to the corrosion. With Fe-Al alloys, fluxing proceeded at a considerable rate in the early stage, but corrosion was still dominated by direct growth of oxides on the metal surface at longer periods of time. The difference in the corrosion mechanism of pure iron and of Fe-Al alloys was thought to be related to the difference in oxygen pressure at the oxide/melt interface. In the series of reactions, SO 3 was the main oxidant. SO 2 released from the reduction of SO 3 caused the formation of sulfides in the scale, and sulfides contributed a great deal to the accelerated corrosion. The effects of temperature, content of ( SO 2 + SO 3) in the atmosphere, and aluminum content in the alloys were discussed.