An overflow-type wetted-wall MFC (WWMFC) was developed to generate a stable voltage from acetate-based substrates. The maximum power density of 18.21 W/m(3) was obtained. The power generation showed a saturation-type rrelationship as a function of initial COD, with a maximum power density (P(max)) of 18.82 W/m(3) and a saturation constant (K(s)) of 227.4 mg/l. Forced air flowing through the cathode chamber had a negligible effect on power generation. Influent flow rate could greatly affect the power generation. The maximum power density was increased by 72.8% when the influent flow rate increased from 5 to 30 ml/min. In addition, increasing ionic strength did not affect the power density and internal resistance. Oxygen could be restrained to diffuse into the anode chamber effectively in the overflow-type WWMFC. And the overflow-type WWMFC could be scaled up conveniently in practical application. (C) 2008 Elsevier Ltd. All rights reserved.