An experimental system consisting of a dual chamber microbial fuel cell was constructed using simulated molasses wastewater as the inoculum and anode substrate, carbon cloth or carbon felt as the cathode base, and MnO₂ as the oxygen reduction catalyst for cathode. By testing and analyzing the output voltage, power density, and COD removal rate of the microbial fuel cell, the effects of the MnO₂-modified cathode on power generation and wastewater treatment of microbial fuel cells were studied. The steady output power density of the microbial fuel cell with carbon cloth cathode were 6.8 and 10.33 mW/m², respectively, before and after modification by MnO₂, that is, the power density of the microbial fuel cell with MnO₂-modified carbon cloth was increased by 51.91% more than that of unmodified carbon cloth. The stable output power density of the microbial fuel cells with carbon felt were 3.6 and 31.37 mW/m², respectively, before and after modification by MnO₂, that is, the power density of the microbial fuel cell with MnO₂-modified carbon felt was increased by 771.4% more than that of unmodified carbon felt. The results show that the electricity generation capacity and the wastewater treatment effect of the microbial fuel cell using molasses wastewater as the anode substrate can be improved significantly by using inexpensive MnO₂ as the cathode modifier.