Nano goethite with contents of 0, 2.5%, 5.0% and 7.5% (mass percentage) were added into activate carbon powder (AC) and rolled onto stainless steel mesh to fabricate new anodes for microbial fuel cells (MFCs). The maximum power density of MFC with 5.0% alpha-FeOOH (693 +/- 20 mW m(-2)) is 36% higher than that of the AC control (508 +/- 40 mW m(-2)). Based on the decrease of charge transfer resistance and the increases of both exchange current density and anodic peak current in electrochemical impedance and polarization tests, the addition of nano alpha-FeOOH kinetically promotes the extracellular electron transfer between bacteria and the electrode. The increase of constant-phase element and the decrease of Warburg element show that alpha-FeOOH enhances both the capacitance and diffusion condition on the surface of anode. However, the excess alpha-FeOOH of 7.5% incurs a negative effect on surface conductivity, capacitance and diffusion, probably due to the adsorption of biogenic Fe(II) on the anodic surface. (C) 2012 Elsevier B.V. All rights reserved.