Microbial fuel cells (MFC) are a promising system to simultaneously accomplish the goal of energy production and wastewater treatment. In the MFC, the cathode plays an important role in achieving high power density and thereby improving the cell performance. In the cathode, an allotrope of carbon [activated carbon, graphite, multi-walled carbon nanotubes (MWCNTs)] is commonly used as a support material for catalysts, such as Pt. Here we show the improved performance of single-chambered MFC (sMFC) using hydrothermally synthesized α-manganese dioxide nanotubes (MnO2-NTs) as the catalyst and graphene as the support in the cathode. With a fixed MnO2-NTs loading, a maximum volumetric power density of 4.68 W m−3 was achieved from the sMFC with MnO2-NTs/graphene, which is higher than that of MnO2-NTs/MWCNTs (3.94 W m−3) and MnO2-NTs/Vulcan XC (2.2 W m−3) composite cathodes, but marginally lower than that of the benchmark Pt/C cathode (5.67 W m−3). The MnO2-NTs/graphene composite also showed a higher oxygen reduction reaction (ORR) activity than the MnO2-NTs/MWCNTs and MnO2-NTs/Vulcan XC composites implying that the former is a better catalyst than the later two. This study demonstrates the high ORR activity and high power generation ability of the cost-effective MnO2-NTs/graphene composite and makes it a potential cathode material for the replacement of expensive Pt in constructing large-scale MFC for wastewater treatment and bioelectricity production.