PURPOSE: To maintain a high battery characteristic during a prolonged operation of a molten-carbonate-type fuel cell by decreasing the speed of the elution of nickel from a cathode electrode material by using the carbonate of an alkaline earth metal as a part of a molten carbonate constituting the electrolyte.

CONSTITUTION: A molten-carbonate-type electrolyte for a fuel cell principally consists of Li2CO3 and K2CO3 and contains at least one carbonate of an alkaline earth metal selected from the group consisting of CaCO3, BaCO3 and SrCO3. This electrolyte is caused to be held in a supporting member consisting of a compound such as LiAlO2 to form an electrolyte layer. It is preferable that the content of LiAlO2 is about 30∼50%, that the total content of Li2CO3 and K2CO3 is at least about 30% and that the content of the carbonates of alkaline earth metals is below 20%. The use of this electrolyte layer enables the formation of a cheap Ni-system-alloy cathode electrode as well as the reduction of the cost of the whole fuel cell.