Single-crystalline CuO nanosheets with the monoclinic structure have been successfully prepared from a layered precursor (coppert(II) acetate hydroxide) in aq NaOH solution by microwave heating or hydrothermal method at 100-200degreesC. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED).