A rigorous numerical model is developed to simulate the dynamic performance of a stacked molten carbonate fuel cell with commercially realistic dimensions. The model takes account of gas stream utilization due to electrochemical reaction, conductive heat transfer between cell hardware and gas streams, energy transfer accompanying mass addition to the bulk streams, and in-plane heat conduction through the cell hardware. The over-potential is calculated using the resistance as a function of temperature and composition of chemical species from literature. It is shown that for a step increase in the current load the output voltage falls at once to a considerable degree and then gradually recovers to the steady state level. The sluggishness of the response is mainly due to the slow dynamics of cell temperature. Therefore, control of cell temperature is necessary to stabilize the response of output voltage under varying current-load situations.