Vertically aligned TiO2/SrTiO3 core-shell heterostructured nanowire arrays with different shell thicknesses (5-40 nm) were fabricated on fluorine-doped tin oxide substrate via a hydrothermal process.Microstructural characterization demonstrated that the TiO2 nanowires were uniformly coated by the singlecrystal SrTiO3 shell,where continuous and large-area interface could be clearly observed.By this means,significantly enhanced photoelectrochemical water splitting properties (0.78 mA·cm-2 at 1.23 V vs.RHE) were successfully realized in well-designed sample (with a shell thickness of 5-10 nm) compared with those of pristine TiO2 (0.38 mA·cm-2 at 1.23 V vs.RHE).The improvement of photoelectrochemical properties was attributed to the improved charge injection and charge separation,which are calculated by the results of water oxidation and sulfite oxidation measurements.Based on these results,a mechanism was proposed that SrTiO3 shell acted as an electron-hole separation layer to improve the photocurrent density.On the other hand,the sample with an over-thick SrTiO3shell (20-40 nm) exhibited slightly reduced photoelectrochemical properties (0.66 mA·cm-2),which could be explained by the increase of the recombination rate in the thicker SrTiO3 shell.This work provided a facile strategy to improve and modulate the photoelectrochemical performance of heterostructured photoanodes.