Partially reduced ZnO nanorod arrays (NRAs) were synthesized in a reducing reagent of NaBH4. The NaBH4 treatment substantially increased the density of oxygen vacancies. The obtained materials were characterized by a field emission scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy and UV-vis absorption spectra. The photocatalytic activity of the resulting samples was evaluated by degradation of methylene blue (MB) under UV light irradiation. The ZnO NRAs with a partially reduced surface exhibited enhanced photocatalytic activity. The improvement was ascribed to the introducing oxygen vacancies in ZnO by NaBH4 treatment. The increased surface oxygen vacancy decreased the surface recombination centers, and improved the charge separation efficiency, thus enhances the photocatalytic activity. Furthermore, we found that moderate treatment enhanced photocatalytic activity. However, with longer time of treatment, bulk oxygen vacancies appeared, which would cause a reduced activity. (C) 2014 Elsevier B.V. All rights reserved.