Electrochemical and photoelectrochemical behaviour of anodized titanium sheets has been investigated. It has been shown that, on a TiO 2 electrode, reduction of oxygen into hydrogen peroxide can take place. Under illumination at rest potential, we have simultaneously the photo-induced anodic oxidation of water into oxygen and the reduction of oxygen into hydrogen peroxide. This H 2O 2 formation is a real photosynthesis reaction on a semi-conductor electrode.