Carbon nanotubes (CNTs) have unique physical / chemical properties including a high surface-area-to-volume ratio, high electrical/thermal conductivity, excellent electrochemical characteristics, and mechanical and chemical stability. This work utilizes CNTs in miniaturized microbial fuel cells (MFCs) to reduce the high internal resistance, one of the significant bottlenecks to improving the power density of the MFC. Three types of CNT electrodes, VACNT (Vertically Aligned Carbon Nano-Tube), RACNT (Randomly Aligned Carbon Nano-Tube), and LBL (Layer-By-Layer) CNT, were evaluated as anodes for miniaturized MFCs, demonstrating biocompatibility, high power density and efficiency. Areal and volumetric power densities of 113 μW/cm2 and 4.52 mW/cm3, respectively, are presented; the highest ever reported among all miniaturized MFCs with CNT anodes to date more than 11.5 times the previous record. Additionally, a coulombic efficiency (CE) of 60%-80% is achieved, significantly higher than existing miniaturized MFCs. High power density and CE may support the miniaturized MFC as a strong candidate in sub-100 μW applications.