Abstract: Nanopowder copper oxide (CuO) crystals have been successfully prepared by decompose of the precursor which was made from the solid state reaction of CuSO4·5H2O and Na2CO3 in the solvent of ethylene glycol under microwave irradiation and then be washed. Then, the precursor was calcined at 600 ℃ for 1 h to obtain nanopowder CuO. The precursor was characterized by TG-DTA at a heating rate of 10 ℃/min in dry air to determine the thermal decomposition and crystallization temperature which was found to be at ～550 ℃. The calcined nanopowders CuO were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fourier transmission infrared (FT-IR) spectroscopy. The results show that the nanopowder CuO consisted of the mixture of nanoparticles with particles size of 30-50 nm,and the average diameter of the particles was about 40 nm.