Decreasing the shell thickness of TiO2 hollow spheres is a promising route to achieve an overall enhanced photocatalytic performance. However, in traditional synthetic approaches, the thin shell can not guarantee the structural stability of the TiO2 hollow spheres in the following calcination process to achieve a high degree of crystallinity. In this paper, ultrathin porous TiO2 hollow spheres with good structural stability, high degree of crystallinity as well as in small grain size were prepared through a novel etching and reconstruction route using amorphous SiO2/TiO2 hollow spheres as precursor. With hot water as etchant, the removal of SiO2 leads to the reconstruction of TiO2 hollow spheres and receiving a thinner and thinner shell. Such thin shell enables the exposure of more catalytic active sites of TiO2 nanocrystals and the improved photogenerated charge transfer and separation. Meanwhile, the residual SiO2 on the TiO2 shell protects the TiO2 nanocrystals from growing larger during high-temperature calcinations. The as-obtained ultrathin porous TiO2 hollow spheres exhibited enhanced photocatalytic activity in hydrogen production from water in comparison with those with thicker shell. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.