Low melting point eutectic salt mixtures are developed as potential candidate for thermal energy storage applications. Thermal conductivity of the ternary eutectic LiNO3-NaNO3-KNO3 salt mixture in the solid state was determined using a simple inverse method. The inverse method was verified for two metal alloys and a HITEC庐 heat transfer salt, and the thermal conductivities were in excellent agreement with those of the literature data. Thermal conductivity of the ternary eutectic salt mixture in the solid state showed a non-linear behavior with temperature.