Electrochemical behaviour of La(III)/La and Pr(III)/Pr systems has been studied in LiF-CaF2 media (79.5%-20.5%) on inert and reactive electrodes in the 820-930°C temperature range using cyclic voltammetry, square wave voltammetry and open-circuit potentiometry. Experimental results show that La(III) and Pr(III) are reduced into metal in a one-step and diffusion controlled process, exchanging 3 electrons, at 0.08 and 0.15 V vs. LiF/Li respectively. Physico-chemical and thermodynamic data such as diffusion coefficients, standard potential, activity coefficients, have been determined. Effect of oxide additions have been investigated and leads to precipitation of LaOF and PrOF species. Alloys formation by reactive electrodeposition on Ni, Cu and Fe electrodes has also been evidenced and their Gibbs energies determined.