Abstract: Reasonable selection of molten salt systems is crucial in the industrial production process of the rare earth metal industry prepared by electrolysis. The density, surface tension and conductivity of LaCl₃-KCl molten salt of different ratios at 1 073—1 223 K were determined by the Archimedes method, tube pulling method and continuous variable conductivity cell constant method (CVCC). The results show that as the temperature increases, the density (ρ) and interface tension (σ) of the LaCl₃-KCl molten salt of the same component decrease, while the conductivity (κ) gradually increases. At the same temperature, with increasing LaCl₃ content in the molten salt, the density and interfacial tention increase, while the conductivity gradually decreases. The empirical formulas for density, interface tension and conductivity are, ρ=a-b×T×10^-3, σ=a-b×T×10^-3, κ=A+B×T×10^-3+C×T²×10^-6, respectively. The change law of the physicochemical properties of molten salt with temperature and components is clarified, which provides a scientific basis for the preparation of lanthanum and its alloys by molten salt electrolysis.