We designed an efficient direct biomass fuel cell (BMFC) anode and prepared a nanocomposite [base electrode/mesoporous n-semiconductor (SC) thin film/metal thin layer]. A Pt thin layer was photodeposited onto a mesoporous 20-mu m thick TiO2 thin film having a roughness factor of 2000, which was coated on an F-doped tin oxide/glass base electrode (FTO). This anode/catalyst nanocomposite was efficient at decomposing aqueous solutions of glucose and other biomass-related compounds in combination with an O-2-reducing cathode the other side of which was exposed to ambient air. The nanocomposite exhibited sharp optimum conditions at the atomic ratio of Pt/Ti = 0.33 in the BMFC, generating high electrical power of 2 mW cm(-2) without any light irradiation or bias potential when using a 1 M glucose aqueous solution. This output power is 20 times as large as that generated by a mesoporous TiO2 film anode under UV-light (18 mW cm(-2)) irradiation. At this ratio, the coated Pt specifically exhibited metallic luster, and its average Pt thickness on the mesoporous TiO2 nanostructure was calculated to be 0.40 nm. The high BMFC activity was interpreted by the simultaneous Schottky-junction/Ohmic contact nature of the nanocomposite. Other biomass compounds such as sucrose, ethanol and polysaccharides were also effective as direct fuels for the BMFC. Immediately after soaking this composite anode without a cathode in a glucose aqueous solution, continuous evolution of H-2 bubbles was observed from the anode surface. The electrical power generation and H-2 production are easily changed by connecting and disconnecting a cathode, respectively. Based on a simple design and calculation, the present system with glucose fuel has the potential to construct a module stack of 2 kW m(-3). Simultaneous material/energy circulation by using the BMFC with biomass and its waste fuel is proposed for application in future social systems.