Cathode dissolution is a major problem for the development of the molten carbonate fuel cell. In order to evaluate the stability of the cathode, the solubility of has been measured for several compositions of molten alkaline carbonates in the pressure range from 10−5 to 1 atm and the temperature range from 873 to 1023 K. The solubility depended on the pressure, although the solubility of was independent of either or pressure. In any composition of the Li/K and Li/Na carbonate melts, the acid dissolution has been observed at higher pressure and the basic dissolution has been observed at low pressure. was found to be more stable in Li rich or Li/Na melts than in the Li/K eutectic melt.