A membrane-free fluidized-bed microbial fuel cell (FB-MFC) was applied to investigate the effects of fluidization parameters on its electrogenesis capacity. Active carbon particles were found to significantly decrease the start-up time and increase the output voltage of the FB-MFC. The fluidization behavior of the active carbon particles in the FB-MFC reactor is one of the key parameters that influence the generation of electricity. With the FB-MFC operating under optimal conditions, maximum power density with minimal internal resistance of the MFC could be obtained. The FB-MFC could be operated in large-scale wastewater treatment processes with high chemical oxygen demand removal efficiencies.