In this study, we demonstrate the effect of iron sheet on the output power of sediment microbial fuel cells (SMFCs). An SMFC with iron sheet present, but not in the circuit (SMFC-GF-iron) displayed a maximum power density of 63 mW m(-2), whereas we find 37 mW m(-2) for that SMFC with the iron sheet not present (SMFC-GF). Furthermore, the SMFC with an iron sheet in the circuit (SMFC-iron) had a maximum power density of 170 mW m(-2). The effect of sheet iron, out of the circuit, was to improve the iron reduction microbial activity, while, within the circuit, it produced a large number of electrons from the electrochemical corrosion yielding higher power production. The study suggests that the addition of iron sheet to an SMFC is an easy and effective method for enhancing the output power of SMFCs. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.