A biophotofuel cell (BPFC) generating electrical power directly from aqueous solutions of biomass and its related compounds with simultaneous photodecomposition and cleaning was investigated. The BPFC had a nanoporous TiO2 photoanode and an O-2-reducing cathode. As long as the compounds were either liquid or water-soluble they were photodecomposed and generated electrical power simultaneously. Various biomasses and related compounds such as glucose, amino acids, polysaccharides, proteins, lignin derivatives, cellulose derivatives and some polymers were investigated in the BPFC. Glucose was photodecomposed almost completely into CO2 under O-2 within 20 h while generating electrical power. The incident photon-to-current conversion efficiency (IPCE) value of a 0.5 M glucose solution in the BPFC under 02 was 29% based on the incident monochromatic light at 350 nm (intensity 3.6 MW cm(-2)). A glycine aqueous solution could be decomposed photochemically into CO2/N-2 in a nearly stoichiometric 4:1 (CO2:N-2) molar ratio. The photodecomposition yield of 0.01 wt% lignosulfonic acid sodium salt was 86.5% in 24 h as estimated from the CO2 evolved. The cellulose (sulfate) gave similar BPFC characteristics under air as under 1 atm O-2. Among the compounds the highest V,,c (open circuit voltage) value was 0.90 V for glutamic acid and phenylalanine.