We constructed a bio-solar cell based on photosynthesis. The bioanode comprises thylakoid membranes from spinach on carbon nanotubes immobilized on a gold-spattered indium tin oxide electrode. [Ru(NH3)(6)]Cl-3 was used as a soluble mediator. The bioanode exhibited a photocurrent density of 180 mu A cm(-2) at 0V vs. Ag vertical bar AgCl vertical bar sat. KCl. The biocathode comprises bilirubin oxidase for direct-electron-transfer-type bioelectrocatalytic O-2 reduction. The cell was constructed without a separator and exhibited an open-circuit voltage of 0.61V and a maximum power density of 50 mu W cm(-2).