The long startup time and low current density of biocathodes limit the application of microbial electrosynthesis systems for CO2 reduction to CH4. Herein, we reported an approach to accelerate the startup and enhance the current density of CH4-producing biocathodes through reversing the polarity during the startup period. A bioanode was first developed at -0.2 V vs. SHE with acetate as electron donor, and then worked as a bio-cathode by reversing the potential of electrode to -0.5 V us. SHE. The results showed that the startup time of the biocathode reversed from the bioanode (similar to 18 days) was shortened by approximately 40% in contrast to that (>30 days) of the control biocathode started up with a constant potential of -0.5 V vs. SHE. In addition, the maximum CH4 production was increased by 1.2 +/- 0.2 times than that of the control biocathode. The results suggested that the "reversed" biocathode possessed a thicker biofilm and higher biomass content than the control biocathode. Our results showed that polarity reversal was an efficient approach for the startup and performance enhancement of CH4-producing biocathodes in microbial electrosynthesis systems. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.