Electrochemical impedance spectroscopy (EIS) together with thermogravimetric techniques were employed to study the corrosion of iron and Fe-Cr alloys containing 5, 10, 20 and 25 wt.% Cr respectively in a molten eutectic (Li,K)(2)CO3 mixture at 650 degreesC. The Nyquist plots for the corrosion of iron and Fe-Cr alloys in the melt are similar, and are all composed of a small semicircle at high frequency and a large semicircle at low frequency. The radius of the semicircle at low frequency, which can be used to evaluate the corrosion resistance of the alloys, is significantly larger for Fe-20Cr and Fe-25Cr than for Fe, Fe-5Cr and Fe-10Cr. The Cr-rich alloys undergo slower corrosion than iron and the Cr-poor alloys: this is further confirmed by the thermogravimetric results and is due to the formation of Cr-rich scales. An equivalent circuit of oxide capacitance in series with the double-layer capacitance was proposed to describe the impedance spectra.