In this study, two inexpensive semicoke and activated carbon packed bed biocathode were developed for oxygen reduction in microbial fuel cells (MFCs). These two materials were compared with two commonly used biocathode materials graphite and carbon felt in terms of material characteristic, power density, biomass density and price-performance ratio. MFCs with semicoke and activated carbon biocathode produced a maximum power density of 20.1 W/m(3) (normalized liquid volume in cathodic compartment) and 24.3 W/m(3), respectively, compared to 14.1 and 17.1 W/m(3) obtained by MFCs with graphite and carbon felt biocathode, respectively. The bacteria attached on biocathode played a major role in oxygen reduction for all the materials investigated. The material cost per Watt produced for semicoke and activated carbon biocathode is only 2.8% and 22.7% of that for graphite biocathode, respectively. These two inexpensive carbon materials, especially semicoke, are very cost-effective biocathode materials for future large scale MFCs. (C) 2011 Elsevier Ltd. All rights reserved.