Magnesium refining processes are typically based on the use of fluxes, most of which contain MgCl2, KCl, NaCl, CaCl2, or BaCl2. These fluxes separate the surface oxides, gases, or other contaminates from the metal. The most important physical and chemical properties of a salt melt are the fusibility, density in the operating temperature range (920–1023 K), and viscosity. Therefore, in this study, the physical and chemical properties of various molten salts were examined to find a new refining flux with a low melting point, low viscosity, high reactivity, and good melt protection using thermodynamic calculations and various experiments using inductively coupled plasma emission spectroscopy, scanning electron microscopy-energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. In addition, the effects of the chemical composition of the flux, amount of flux, fluxing temperature, and stirring time and intensity on the refining process of molten magnesium were studied. The optimized conditions for the Mg refining process resulted in a ternary flux system with 31 mass% MgCl2, 60 mass% KCl, and 9 mass% NaCl, through the addition of 1 mass% CaF2 and 5 mass% MgO, and stirring at 150 RPM for 15 min at 953 K.