In summary, well-defined 3D hierarchical ZnO microspheres have been successfully synthesized via a facile solvothermal route with the assistance of HEPES, which acts as a directing agent in the assembly of rod-like building blocks into hierarchical ZnO nanostructures. TEG, with proper viscosity, also contributes to the fabrication of porous ZnO microspheres. Moreover, hierarchical ZnO microspheres exhibits outstanding photocatalytic activity for MB degradation under UV light irradiation, which might be ascribe to its large BET surface area and ideal pore volume.