A module part of a class centralized molten carbonate fuel cell/gas turbine (GT) combined system has been tested. Since the designed (GT) working pressure is , the operating pressure of the module was high . In order to realize a high steam-reforming efficiency of the fuel gas under high-pressure operation, the module has an additional adiabatic reformer, which changes the remaining in the exhausted anode gas to . Using a 125-cell stack, the module was operated and the performance of the stack was evaluated; the partial pressure of the cathode inlet gas was kept low during the operation. The maximum operating current density of the stack was limited to ; however, the maximum total steam-reforming efficiency of the fuel gas was 96% in the module. The heat loss of the module was evaluated in the pressure swing test. Using these operation results, the efficiency of the module, at the designed operating current density of , was estimated; the result was 39.6% low heating value (LHV) by applying the normal cell performance, whereas 44.4% LHV by applying the best performance cell. The module efficiency of 44.4% LHV corresponds to the system’s net efficiency of 48% high heating value in the system.