Mixed-phase TiO₂ nanostructures are synthesized by hydrothermal treatment of anodized TiO₂ nanotubes. The growth of rutile nanorods on the anatase nanotubes can greatly expedite the electron–hole separation and transportation, enhance the light absorption, and also increase the surface area. When used for photocatalytic water splitting, more than three-fold enhancement in photocurrent density is observed for mixed-phase TiO₂ nanostructures, relative to pristine TiO₂ nanotubes.