We evaluate two kinds of solid-oxide-fuel-cell (SOFC)-polymer-electrolyte-fuel-cell (PEFC) combined systems by numerical simulation to investigate the effect of the fuel feeding method. In one, fuel for the system is reformed by using exhaust heat from the SOFC and is separately supplied to the SOFC and PEFC (parallel SOFC-PEFC system). In the other, fuel is fed to the SOFC first and then SOFC exhaust fuel is fed to the PEFC (series SOFC-PEFC system). The quality of the fuel gas in the SOFC is better in the latter system, whereas the quality of the fuel gas in the PEFC is better in the former. We demonstrate that larger PEFC output can be obtained in the parallel SOFC-PEFC system, since more steam, which is included in the SOFC anode exhaust gas, can be used for the reforming of the fuel for the PEFC. We show that the series SOFC-PEFC system provides higher electrical efficiency because the fuel gas quality has a stronger influence on the electromotive force in the SOFC than in the PEFC. (c) 2005 Elsevier B.V. All rights reserved.