A mathematical model was developed to simulate the performance of a molten carbonate fuel cell (MCFC) 5 kW class stack. In the modeling calculations, the average current densities of each cell were adjusted to be same for all cells in the stack. In this procedure the operating voltages of each cell were decided. Temperatures of matrixes with an electrolyte increased to a maximum value at the 7th cell. Because the temperatures of the 1st and 9th cells were lower than those of the other cells, the operating voltage of these cells was lower than those of the other cells. Compared to the measured temperature distributions, the calculated results were quite low near the gas entrance. The measured data of the temperature of the matrixes with an electrolyte and the power were estimated well with the modeling calculations. The current density distributions in all cells from the model calculations were similar.