Electrochemical impedance spectroscopy (EIS) technique was employed to study the corrosion of B-1900 alloy at 800degreesC in air in the presence of a solid Na2SO4 and a molten 25 wt.% NaCl-75 wt.% Na2SO4 film, respectively. It was found that the Nyquist plot for the corrosion of the alloy was composed of one capacitive loop. The medium resistance decreased and then increased with experimental time in the presence of the Na2SO4 film, while the charge transfer resistance reduced with time, which indicated the change of surface deposit from a solid state to a molten state and the occurrence of fast corrosion. As compared with the solid Na2SO4 film, the presence of the molten NaCl-Na2SO4 film gives rise to smaller impedance. Impedance model was proposed to explain the corrosion behavior of the alloy. (C) 2003 Elsevier Ltd. All rights reserved.