BACKGROUND: The biocathode is proving to be a promising feature for development of the microbial fuel cell (MFC), although much work remains to be done to increase its power generation. This study aimed to enhance the performance of a biocathode by applying selected cathode potential. RESULTS: When five two-chambered MFCs were operated at selected cathode potentials of 142, 242, 342, 442, or 542 mV (vs standard hydrogen electrode), those MFCs with selected potentials lower than 342 mV could start up, and the highest power density of 0.11 W m(-3) was obtained at a selected potential of 242 mV. An inner-biocathode MFC was then constructed and operated at a start-up cathode potential of 242 mV for 30 days. The open circuit cathode potential increased from 477 +/- 9 mV to 572 +/- 8 mV compared with the potential of the initially abiotic cathode, resulting in an increase in the maximum power density (4.25 +/- 0.16 W m(-3)) of 106%. In addition, tests of continuous operation showed that a loading rate of 135 mg COD L-1 d(-1) was optimal for obtaining maximum power generation in the system developed for this study. CONCLUSION: The results indicated that an optimal cathode potential of 242 mV enhanced the performance of a biocathode using oxygen as the electron acceptor. (C) 2009 Society of Chemical Industry