Electrochemical and spectroscopic properties of Tb(III) in molten LiCl–KCl eutectic at high temperature were investigated by cyclic voltammetry and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The diffusion coefficient of Tb(III) and the formal standard potential of Tb(III)/Tb 0 were determined to be 2.06±0.4×10 −5 cm 2 s −1 and −2.83±0.03V vs. Cl 2 /Cl − at 887K, respectively. Additionally, visible fluorescence of Tb(III) due to the electronic transitions from 5 D 3 and 5 D 4 to 7 F J was observed and measured by TRLFS for the first time. These results provide the first fluorescence spectroscopic evidence for a direct in situ quantification of Tb(III) in the high temperature molten salt system.