Cobalt sulfide quantum dots (CoSx QDs) modified TiO2 nanoparticles are prepared with a precipitation-deposition method using TiO2, cobalt acetate and sodium sulfide as the precursors. CoSx QD acts as an effective cocatalyst, which accelerates the transfer of the photo-generated electrons and serves as the active site for the reaction between electrons and H2O, thus enhancing the separation of the e(-)/h(+) pairs and the photocatalytic H-2 production activity of TiO2. The amount of CoSx exhibits an optimum value at about 5% (mole ratio to TiO2), at which the H-2 production rate achieves 838 mu mol h(-1) g(-1) using ethanol as the sacrificial reagent. This exceeds that of the pure TiO2 by more than 35 times. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.