The controlled synthesis of hierarchical CuO nanomaterials in a solution phase has been realized with high yield at low temperature using copper acetate hydrate and NaOH as starting materials with the assistance of surfactant under hydrothermal conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy (UV-Vis) were used to characterize the products. It was shown that the hierarchical CuO nanoarchitectures were formed through aggregation of tiny single-crystal CuO nanorods. Experiments demonstrated that the morphology of CuO products was significantly influenced by hydrothermal temperature and reaction time. A rational growth mechanism based on oriented attachment was proposed for the selective formation of the hierarchical CuO nanoarchitectures. Our work demonstrated the growth of hierarchical CuO nanoarchitectures built from onedimentional nanorods through a one-step solution-phase chemical route under controlled conditions. In addition, The UV-Vis spectrum of the hierarchical CuO nanoarchitectures showed large blue shift because of the quantum size effect.