BACKGROUND: The utilization of mixed monosaccharides commonly found in the hydrolysates of lignocellulosic biomass was evaluated for power generation in single chamber air cathode mediator-less microbial fuel cells. RESULTS: A similar voltage generation pattern was observed for all the MFCs with different monosaccharide combinations and an external resistance of 1000 Omega. However, the different monosaccharide utilization rates ranging from 212 mg L-1 h(-1) to 389 mg L-1 h(-1) indicate the presence of preferential utilization of different monosaccharides. Three volatile fatty acids (VFAs), including acetic, propionic and butyric acids were detected as the main intermediates, which were generated mainly through a fermentation process. CONCLUSION: VFAs produced from initial monosaccharides contributed to a significant portion of the total electricity generated, and the fermentation process out competed the electricity generation process when a mixed bacterial culture was used. (C) 2011 Society of Chemical Industry