This work focuses on the study of photocatalytic and antibacterial activity of TiO2 nanoparticles synthesized by laser ablation in water. The nanoparticles have a log normal size distribution with a mean diameter of 34 nm and are composed by a mixture of small crystallites and disordered TiO2; they show good stability and are extremely pure. High photocatalytic (Methylene-Blue dye discoloration under UV illumination) and antibacterial (tested on Escherichia cod) activities comparable to that of commercial nanoparticles under the same experimental conditions were observed. Optical and structural properties were correlated to the photocatalytic and antibacterial activity, and compared to that of commercial TiO2 nanoparticles. An explanation of the high photo-activity yield is proposed taking into account the nanoparticles structure resulting from the peculiar synthesis procedure. (C) 2014 Elsevier B.V All rights reserved.