For better understanding of the behaviors of MgO and BaO within glass frit PF798, which is a candidate for use in immobilization of radioactive nuclear waste and consisted of 63.6SiO(2), 16.8 B2O3, 4.0Al(2)O(3), 3.0ZnO, 4.4CaO and 8.2Li(2)O in mole pet., oxidation-reduction equilibrium experiments for Fe3+/Fe2+ couple were conducted with the melts of {PF798 + MgO} and (PF798 + BaO) at 1473 K and under a stream of pure CO2 of 1 atm.