This study examined the performances of two double-chamber microbial fuel cells (MFCs) at 25 degrees C and 15 degrees C. After successful startup, the cell temperature of MFC A was decreased from 25 to 15 degrees C, yielding a sudden breakdown of the entire system. Conversely, the MFC B, started up at 15 degrees C, delivering higher power density at 25 degrees C than MFC A at the same temperature. The electrochemical analysis revealed that the MFC B had lower anodic resistance than MFC A. Additionally, a negative temperature dependence of the polarization resistances of the anodic biofilm was noted, a novel phenomenon only reported in this double-chambered study. Microbial analysis showed that the psychrophilic bacteria were enriched in anodic biofilms of MFC B, which likely contributed to the robust cell performance of the present double-chambered MFCs. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.