Phase diagrams of binary mixtures of alkali bis(trifluoromethylsulfonyl)amides have been constructed, and their eutectic compositions and temperatures have been determined. It has been revealed that the molten salt electrolytes having the melting points in the intermediate temperature range (373 to 473) K are easily formed by simple mixing of two kinds of single alkali bis(trifluoromethylsulfonyl)amide salts. The 1:1 or 3:1 double salt is occasionally formed for some binary systems.