Reducing the inner resistances is crucial for the enhancement of hydrogen generation in microbial electrolysis cells (MECs). This study demonstrates that the optimization of the anode arrangement is an effective strategy to reduce the system resistances. By changing the normal MEC configuration into a stacking mode, namely separately placing the contacted anodes from one side to both sides of cathode in parallel, the solution, biofilm and polarization resistances of MECs were greatly reduced, which was also confirmed with electrochemical impedance spectroscopy analysis. After the anode arrangement optimization, the current and hydrogen production rate (HPR) of MEC could be enhanced by 72% and 118%, reaching 621.3 +/- 20.6 A/m(3) and 5.56 m(3)/m(3) d respectively, under 0.8 V applied voltage. A maximum current density of 1355 A/m(3) with a HPR of 10.88 m(3)/m(3) d can be achieved with 1.5 V applied voltage. (C) 2011 Elsevier Ltd. All rights reserved.