The performance of a system consisting of an up-flow anaerobic sludge blanket (UASB) reactor and a microbial fuel cell (MFC) for the treatment of low-strength wastewater and the recovery of energy was evaluated. The UASB reactor (1 L) was continuously fed with raw domestic wastewater under hydraulic retention times (HRT) of 12 and 6 h. The MFC (250 mL) was operated in batch mode and fed with either raw wastewater (HRT = 12 h) or the effluent from the UASB reactor (HRT = 6 h). It was found that the removal of organic matter by the coupled UASB–MFC system (88 % chemical oxygen demand (COD), 75 % total organic carbon (TOC) and 79 % total suspended solids (TSS)) was higher than the levels obtained by the UASB reactor (76 % COD, 66 % TOC and 73 % TSS) and the MFC (60 % COD, 53 % TOC and 40 % TSS) when these were operated individually. The highest power density obtained in the MFC was 176 mW/m2 with 1000 Ω resistance, whereas the coulombic efficiency was 8 %. The UASB-MFC system proved to be a good alternative for the treatment of wastewater and the simultaneous generation of electricity even under substrate limiting conditions, such as low concentration of organic matter in the influent.