Pure TiO2 anatase particles with a crystallite diameters ranging from 4.5 to 29 nm were prepared by precipitation and sol-gel method, characterized by X-ray diffraction (XRD), BET surface area measurement, UV-vis and scanning electron microscopy (SEM) and tested in CO2 photocatalytic reduction. Methane and methanol were the main reduction products. The optimum particle size corresponding to the highest yields of both products was 14 nm. The observed optimum particle size is a result of competing effects of specific surface area, charge-carrier dynamics and light absorption efficiency. (C) 2009 Elsevier B.V. All rights reserved.