Analysis of AC impedance in a molten carbonate fuel cell (MCFC) has been diversified among researchers regardless of the convenience of its measuring. The insufficient understanding of mass transfer processes at the electrodes may be a reason. In this work, the AC impedance analysis was carried out with 100 cm(2) class MCFCs, and simulation based on an equivalent circuit and reported kinetic parameters were conducted. From the cell, two of high and low frequency half circles were observed which represented liquid and gas phase mass-transfer effects, respectively. The simulation successfully represented that the liquid phase mass-transfer was due to the concentration of active species in the cathode while the gas phase mass-transfer was mostly attributed to the gas flow rate in the anode. For the gas flow rate effect, the mass transfer resistance was a function of boundary layer thickness because the flow at both electrodes was fully in the laminar region. (C) 2016 Published by Elsevier B.V.