Cu2PO4OH with various hierarchical morphologies were synthesized using a hydrothermal method by simple adjusting the pH value and temperature. The prepared powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, fourier-transform infrared spectroscopy (FT-IR), and UV-Vis diffuse reflectance spectroscopy. It was found that overall morphologies of Cu2PO4OH were varied from micro-rods to walnut-like microspheres as increasing the initial solution pH value and their size of the assembled crystallites was smaller at lower temperature. From the FT-IR and Raman analysis, the incorporation of the hydroxyl ions (OH-) into the crystal structure plays important roles to their crystallization process, and finally affects their morphologies. Moreover, the optical absorption properties of the Cu2PO4OH were strongly related to their morphologies. The photocatalytic activity of Cu2PO4OH with various morphologies was also investigated via the degradation of rhodamine B (RhB) dye solution under visible light irradiation (lambda > 410 nm). The walnut-like microsphere assembled with nanoparticles exhibited higher photocatalytic activity due to the higher optical absorption as well as a higher surface area.