Zinc oxide (ZnO) microstructures were successfully prepared by hydrothermal synthesis with PEG4000 at 120°C for 24 h. The crystalline phase and morphology of ZnO microstructures were characterised by X-ray diffraction and scanning electron microscopy. The results show that the rod-like, flower-like and dumbbell-shaped ZnO microstructures can be easily controlled by varying the amount of PEG4000. The photoluminescence spectra of ZnO microstructures with different morphology at room temperature show four emission peaks at about 362, 389, 421 and 487 nm. The photocatalytic activities of ZnO microstructures are evaluated by degradation of methylene blue (MB) under ultraviolet light irradiation, and the degradation rates of MB with rod-like, flower-like and dumbbell-shaped ZnO microstructures reached 94.8, 95.4 and 70.9%, respectively.