Abstract This work presents the electrochemical properties of gadolinium (Gd), a significant rare earth element in spent nuclear fuel (SNF), in the LiCl KCl eutectic. To explore thermodynamic properties of Gd at the liquid gallium (Ga) electrode, experiments were performed both on the inert tungsten (W) and liquid gallium (Ga) electrode at different temperatures in a range from 723 to 823 K, which show that the Gd metal can be oxidized to Gd (III) by exchanging of 3 electrons. Electrochemical techniques including cyclic voltammetry (CV), open circuit potential (OCP), potentiostatic electrolysis and galvanostatic electrolysis were utilized to detect the electrochemical behavior and evaluate standard apparent potential of the Gd(Ⅲ)/Gd couple, and E Gd(Ⅲ) / Gd * = − 3.456 + 6.2 × 10 − 4 T ( ± 0.046 ) ( vs C l 2 / C l − ) is obtained. In addition, electromotive force (EMF) and coulometric titration were employed to calculate the activity and activity coefficient of Gd in metal Ga. After calculation, the activity is 1 . 791 × 10 − 15 at 723 K and function of activity coefficient and temperature is lg γ = 3.485 − 10927 / T ( ± 0.0875 ) .