A floating microbial fuel cell (FMFC) has been designed and its performance has been evaluated for 153 days. The power output gradually increased to a maximum value of 390 mW/m(3) at 125 days. The polarization resistance of the anode (R-p(a)) changed with operating time reaching a minimum value at 125 days, while the polarization resistance of the cathode (R-p(c)) was relatively constant and much smaller than R-p(a). It has been demonstrated that the observed changes of the internal resistance (R-int) and the maximum power (P,) with exposure time were mainly due to the changes of R-p(a). Compared with sediment MFCs for which the anode is embedded in marine or river sediments, the application of the FMFC, which could be installed in a buoy, is not limited by the depth of the ocean. The FMFC has the potential to supply electricity to low-power consuming electronic devices at remote locations. (C) 2012 Elsevier Ltd. All rights reserved.