Separation of hafnium tetrachloride from zirconium tetrachloride by introducing zirconium tetrachloride containing about 2-4 wt percent of hafnium tetrachloride into an electrolytic cell filled with a molten salt and dissolving it to make an electrolytic bath. Running first phase electrolysis which produces zirconium trichloride containing a lower hafnium content than the dissolved zirconium tetrachloride at the cathode. Running second phase electrolysis using the first cathode, but switching the first cathode to become an anode and using a second cathode. Producing zirconium trichloride of a lower hafnium content than the dissolved zirconium tetrachloride at the second cathode. Evolving a gaseous zirconium trichloride at the anode by electrolytic oxidation of the zirconium trichloride produced in the first phase electrolysis. Recovering this evolved zirconium tetrachloride which has a lower hafnium content than the dissolved zirconium tetrachloride and the zirconium trichloride produced at the cathodes. Continuing this second phase electrolysis by changing over polarities of the cathode and the anode, when the concentration of zinc trichloride at the anode decreases to a predetermined concentration when the vapor pressure valve of hafnium tetrachloride, which has become concentrated in the electrolytic bath reaches about 1/10 of that of zirconium tetrachloride in the electrolytic bath. Transferring the hafnium enriched electrolytic bath to a separate vessel and separating it from the molten salt by raising the temperature of the electrolytic bath to a predetermined temperature.