Hydrogen production from aqueous mixture of I - and acetonitrile using dye-sensitized Pt/TiO 2 photocatalyst was investigated under visible light irradiation. It was found that energetically uphill H 2 formation with a high quantum efficiency (~2%) took place using a merocyanine dye-sensitized Pt/TiO 2 photocatalyst and an I - electron donor in an acetonitrile-water mixture (AN:H 2 O=95:5 by volume) under visible light irradiation (λ>440nm). Addition of acetonitrile, which is a good solvent for I - and merocyanine dye, significantly improved H 2 evolution.