CuO nanostructures with various novel shapes were synthesized via a facile hydrothermal method at different reaction conditions using a nonionic surfactant polyethylene glycol (PEG) as the structure-directing template. The products were characterized by powder X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. X-ray diffraction indicated that the products were CuO with a little Cu₂O. SEM showed the various shapes of CuO nanostructures, including clew, gear wheel, and nanowire bundles. The morphology of the CuO nanostructures was determined by the reaction temperature and time. The clew CuO nanostructures with the diameter of about 3 µm were prepared at 150℃ for 10 h. When we increased the temperature to 160℃ for 10 h, the gear wheel CuO nanostructures with the diameter of about 10 μm and the thickness of about 1.5 µm were obtained. CuO nanowires bundles with the diameter of about 80 nm were prepared at 180℃ for 21 h. The results indicated that the clew CuO nanostructures gradually changed to nanowire bundles with increase of the reaction temperature and time. The morphologies were not reported before. The growth mechanism of the CuO nanostructures was also discussed briefly.