TiO₂ nanotube arrays formed on Ti substrate by electrochemical anodization have been converted into TiO₂−SrTiO₃ heterostructures by controlled substitution of Sr under hydrothermal conditions. The growth of SrTiO₃ crystallites on the nanotube array electrode was probed by electron microscopy and X-ray diffraction. As the degree of Sr substitution increases with the duration of hydrothermal treatment, an increase in the size of SrTiO₃ crystallites was observed. Consequently, with increasing SrTiO₃ fraction in the TiO₂−SrTiO₃ nanotube arrays, we observed a shift in the flat band potential to more negative potentials, thus confirming the influence of SrTiO₃ in the modification of the photoelectrochemical properties. The TiO₂−SrTiO₃ composite heterostructures obtained with 1 h or less hydrothermal treatment exhibit the best photoelectrochemical performance with nearly 100% increase in external quantum efficiency at 360 nm. The results presented here provide a convenient way to tailor the photoelectrochemical properties of TiO₂−SrTiO₃ nanotube array electrodes and employ them for dye- or quantum-dot-sensitized solar cells and/or photocatalytic hydrogen production.