Response of a microbial fuel cell under variable load conditions is of paramount importance when it is used for the application of wastewater treatment.In this study，four two-chamber MFCs were started up and evaluated under an external resistance of 50，100，400，1000 Ω，respectively.The results indicated that MFC-50 has the longest log phase for the development of the biofilm while a highest maximum power density can be obtained after start-up.It was also found that the voltages of MFC-100 and MFC-50 dropped and maintained a steady-state when a 50Ω resistance was connected into the electrical circuit，whereas the voltages of MFC-400 and MFC-1000 elevated slowly for ～2 d to the values similar to those of MFC-200 and MFC-50 after the initial abrupt drop under the same loading condition.After the stabilization of the MFCs，the maximum power densities of all the MFCs were comparable and reached 2000 mW·m-2.Further switching the external resistance from a small to large one，no noticeable change in performance can be found.