The temperature and enthalpy vs. composition diagrams of the binary system [xC3H7CO2Li+(1–x)C3H7CO2Rb], where x=mole fraction, were determined by differential scanning calorimetry (DSC). This binary systems displays the formation of two mixed salts with a composition 1:1 and 1:2, which melt incongruently at Tfus=590.5 K, with ΔfusHm=11.6 kJ mol–1, and congruently at Tfus=614.5 K, with ΔfusHm=20.2 kJ mol–1, respectively. The phase diagram also presents an ionic liquid-crystalline phase in a wide temperature range: 95 K.