The growth of particles of lithium aluminate (LiAlO2) as an electrolyte retention material in molten carbonates leads to a decrease in the electrolyte retention ability, and so the performance of the fuel cell deteriorates. We have studied how to improve the material in order to maintain the electrolyte retention ability for a long term in Li/Na carbonates. As a result, we found that zirconia powder added to lithium aluminate keeps the electrolyte retention ability constant for over 7000 h in the alkaline carbonate in a P-CO2 = 0.1 atmosphere.