The vapor pressures of ZrCl4 and HfCl4 over a molten salt mixture of KCl + AlCl3 (1:1.04 mol) + XCl(4) (X = Zr, Hf) was determined in the temperature range of 485-627 K by the transpiration technique. The compositions of ZrCl4 and HfCl4 in the molten salt system were chosen such that it would be useful for vapor phase separation of ZrCl4 from Zr(Hf)Cl-4 by an extractive distillation technique employing KCl + AlCl3 as the fused salt solvent. The relative volatility factor of p(HfCl4)/P-ZrCl4 over the KCl + AlCl3 + XCl(4) (X = Zr, Hf) molten salt systems was determined to be 1.5 in the composition range of 16-30 mol % HfCl4 or ZrCl4. This indicated the possibility of separation of ZrCl4 and HfCl4 by extractive distillation with KCl + AlCl3 molten salt solvent at ambient pressure.