Abstract：The influence of dissolved oxygen in cathode and external resistance on the performance of electricity generation and pollutant removal of microbial fuel cell (MFC) were investigated after successful start-up of a double-chamber denitrifying MFC. The results revealed that, with sodium acetate as electron donor and sodium nitrate as electron acceptor under the ambient temperature of 25℃, the denitrifying MFC was started successfully in 42 days through continuous feeding followed by batch feeding. The oxygen and nitrate could serve as electron acceptor simultaneously when oxygen existed in the influent of cathode. In the lower range of current density, oxygen was the main electron acceptor with a maximum power density of 26.0W/m3NC; as the current density increased to a certain extent, nitrate became the main electron acceptor gradually with a maximum power density of 20.9W/m3NC. The external resistance had little effect on COD removal and denitrifying degree, and the COD removal loading maintained at about 1.2kg/(m3NC·d) with the effluent concentration of NO-2-N below 0.05mg/L; but decreasing the external resistance resulted in improvement of nitrogen removal performance in cathode, and the NO-3-N removal loading reached to 0.111kg/(m3NC·d) when the external resistance was set at 5W.