We have found that Ag-modified La2Ti2O7 with a layered perovskite structure exhibits activity for the photocatalytic conversion of CO2 to CO in pure water. The evolution of O-2 proves that H2O works as an electron donor for the photocatalytic conversion of CO2. CO was generated as the main product, and CO, H-2, and O-2 were produced in stoichiometric amounts. The crystallite size of La2Ti2O7 increased and the surface area decreased with increasing calcination temperature and time. Maximization of the photocatalytic activity of La2Ti2O7 was accomplished by making a trade-off between the crystallite size and surface area. In addition, the loading amount and modification method of the Ag cocatalyst also influenced the amount of CO evolved. An isotope labeling experiment using (CO2)-C-13 confirmed that the origin of evolved CO was not the residual carbon species on the La2Ti2O7 surface, but was rather the CO2 gas that was introduced during the experimental process. (C) 2014 Elsevier B.V. All rights reserved.