The chemical and electrochemical properties of solutions of molybdenum chlorides in the fused LiCl-KCl eutectic were studied at 500-degrees-C. The chemical stability of solutions is an important parameter which must be controlled to ensure reproducible electrochemical measurements. Polarization curves at vitreous carbon electrodes revealed the existence of an electronic exchange between the stable species Mo(III) and Mo(IV) with a standard potential equal to 880 mV vs. the Ag/AgCl reference electrode. The reduction process appeared as a simple irreversible three-electron exchange coupled with significant crystallization problems.