Hematite nanostructures with various thicknesses were prepared for solar water splitting by controlling the HCl concentration in hydrothermal process. Results show that when the thickness increases, hematite will form layered structure on the substrate instead of the continuing growth of nanorods. A single layer of vertical nanorods shows the best performance for solar water splitting while multi-layers of nanorods show worse performance, which can be attributed to bad conductivity between hematite layers revealed by Mott-Schottky plots. Data clearly demonstrate the thickness effect of hematite nanostructures, which can be a key role for the performance of solar water splitting. (C) 2014 Elsevier B.V. All rights reserved.