The molten carbonate fuel cell (MCFC) is working on the basis of high temperature carbonate electrolyte. The molten carbonate, normally liquid at 650oC, provides very fast electrode kinetics at the anode as well as the cathode. The fast kinetics at the electrodes leads to gas-phase transport limitation, thus cell performance is a function of gas feed rate. The feed flow rate affects overpotential at the electrodes as well as cell performance, which can be observed with inert gas step addition (ISA) method. Therefore it allows a novel approach for the performance analysis in the MCFC. This presentation reports performance analysis results of 100 cm2 class MCFC cell with ISA method.