The redox reaction between divalent and trivalent iron species in binary and ternary molten salt systems consisting of 1-ethyl-3-methylimidazolium chloride (EMICl) with iron chlorides, FeCl2 and FeCl3, was investigated as a candidate of the half-cell reactions of novel rechargeable redox batteries based on low temperature molten salt systems. A reversible one-electron redox reaction between divalent and trivalent iron species was observed on a platinum electrode in EMICl–FeCl2–FeCl3 system at 130°C. The voltammetric data indicated that divalent and trivalent iron species were FeCl3 − and FeCl4 − complex anions, respectively. Combined with another proper redox couple, this molten salt system can be utilized in a rechargeable redox battery on account of its low melting temperature and reversible redox reaction.