CuO nanopowder oxide was synthesized by reflux condensation method without any surfactants or templates, using copper nitrate in deionized water and aqueous ammonia solution. The structural, optical and electrical properties of the sample were investigated using X-ray diffraction (XRD), FT-IR, UV–visible spectroscopy and impedance spectroscopy measurements. The X-ray diffraction patterns revealed that CuO nanoparticles (NPs) was formed in pure monoclinic phase and good crystalline quality, whose NPs sizes were of the order 25 nm which an average size can be tailored by the synthesis time. FT-IR spectra of CuO NPs used to detect the possible adsorbed species on the CuO materials. In addition, the peaks at 529 and 604 cm-1 correspond to the characteristic stretching vibrations of Cu-O bond in the monoclinic CuO. The optical absorption property has been determined by UV–visible Spectroscopy in the wavelength range of 200–800 nm which indicate the energy gap (Eg). As result, Eg increases with increasing the synthesis time from 2.72 to 1.87 eV. The complex measurement has been investigated at room temperature, and in the frequency range 40 Hz–100 kHz, showing that Nyquist plots (Z' versus Z'') are well fitted to an equivalent circuit model which consists of a parallel combination of a bulk resistance Rb and constant phase elements CPE. On the other hand, the capacitance and the conductance of CuO NPs have a proportional relationship to the charge transfer and the surface electrode-pallet. These properties make these materials very promising electrode.