Nonafluoropentanoic acid (C4F9COOH; NFPA), which is a typical perfluorinated acid, was decomposed to F- and CO2 with a water-soluble tungstic heteropolyacid photocatalyst, H3PW12O40. The catalytic reaction proceeded in water at room temperature under UV-Vis irradiation in the presence of oxygen. The reaction system produced no trace of environmentally undesirable species, such as CF4 and CF3H. In addition to F- ions, a small amount of a one-CF2-unit-shortened species, heptafluorobutyric acid (C3F7COOH; HFBA), was formed. The reaction mechanism involves precomplexation between [PW12O40](3-) and NFPA and subsequent redox reactions. (C) 2003 Elsevier B.V. All rights reserved.