Abstract: It was investigated that NH₄Cl and HCl were applied to remove oxide ion from LiCl-KCl eutectic molten salt. During removing oxide ion from LiCl-KCl eutectic molten salt, yttria-stabilized zirconia electrode was used to measure the concentration change of concentration of oxide ion. The results show that HCl reacts with oxide ion to generate H₂O, and H₂O escapes from LiCl-KCl eutectic molten salt with unreacted gas HCl. NH₄Cl reacts with oxide ion on the similar principle. Both HCl and NH₄Cl can effectively reduce oxide ion to a low concentration of 10^-5-10^-4 mol/kg in LiCl-KCl eutectic molten salt.