To establish the operating conditions of molten carbonate fuel cells, the relationship between operating variables and the performance of the single cell with the active electrode area of 100㎠ was investigated. The single cell showed the open circuit voltage of 1.13V and the cell voltage over 0.9V at the current density of 150mA/㎠. The performance decreased with the increase of the hydrogen utilization, while the effect of the oxygen utilization turned out to be negligible. The performance increased proportionally to the hydrogen partial pressure of the anode gas, but the highest performance was obtained at the voltage loss estimated from the Nernst equation, and the oxygen gain was 50mV and 90mV at the condition of the open circuit voltage and at the current density of 150mA/㎠, respectively. The cell voltage at the given conditions tended to increase with the increase of the operating temperature, but the increasing rate became smaller above 650℃.