Electrochemical properties of a molten salt based on Bi2O3 with a MgO matrix has been investigated. Melting temperature can be lowered by adding both Li2O and Na2O, while the conductivity is not influenced by the ratio Li2O/Na2O in the System (Bi2O3)(0.7)[(Li2O)(1-x)(Na2O)(x)](0.3). From the EMF measurements of the oxygen concentration cell, the molten salt is found to operate as an oxide ion conductor. Although Bi2O3 is easily reduced in H-2 gas atmosphere, it can be used at least down to 10(-4) atm of oxygen gas partial pressure.