Overload tests that involve setting a bench-scale molten carbonate fuel cell (MCFC) beyond a 100%-gas utilization of fuel or oxidant for 1 s by using the current-pulse method have been carried out to verify the durability and capacity of the MCFC in this particular overload situation. The experimental results show that the MCFC has a good durability and a certain kind of capacity for instantaneous overload. We have built a model to represent the MCFC voltage behavior at overload based on the experimental results; the model is capable of estimating the overload capacity under various operating conditions. When a developer constructs a robust control system for an MCFC power plant to measure the voltage fluctuation of the electric power network or explores the possibility of the MCFC power system using the mitigating function of the voltage fluctuation by means of the instantaneous overload capacity of the MCFC, it is useful to understand the overload capacity of an MCFC from a quantitative perspective and estimate the voltage behavior of an MCFC on overload.