Nickel oxide (NiO)-decorated titanium dioxide (TiO2) heterojunction photodetectors were prepared by two-step anodization. Surface scattering of NiO particles was successfully controlled by varying second-step anodizing voltage, with substantially less clustering of NiO particles on the TiO2 nanotubes (NTs) observed as the voltage increased. Fabricated photodetectors exhibited higher sensitivity to UV light as NiO surface dispersion increased. Electronic bandgap of TiO2 and that of NiO was determined as 3.35 eV and 3.80 eV, respectively. Introduction of NiO particles on well-ordered TiO2 NTs narrowed the bandgap of TiO2, and the difference between work functions of TiO2 and NiO produced sufficient built-in electric field to separate the electron-hole pairs. This led to an enhanced performance of NiO/TiO2 heterojunction photodetectors, which showed high values of responsivity (86 A/W), external quantum efficiency (292%), and detectivity (2.2 x 10(10) Jones) under 365 nm UV light illumination. The valence and conduction band offsets at the interface of the NiO/TiO2 heterojunction were determined as 1.54 eV and 1.99 eV, respectively.