We have studied the effects of the kinetic energy of mass-separated O+ beams on the growth of CuO thin films deposited on unheated MgO(001) and at 510 °C, in energy ranging from 10 to 200 eV by x-ray photoemission spectroscopy, x-ray diffraction, reflection high-energy electron diffraction, and scanning electron microscopy. The films deposited at 510 °C show a full width at the half maximum (FWHM) of 0.06°for the rocking curve through the (111) peak, regardless of the kinetic energy of oxygen ions. CuO has been epitaxially grown on MgO(001) without heating it in a vacuum of 4 × 10−7 Pa. The x-ray diffraction intensity of the CuO(111) increases with an increase in the kinetic energy of O+, and its FWHM approaches that of the CuO film grown at 510 °C. The surface morphology is improved for the films deposited on unheated substrates.