Copper oxide nanoparticles and submicron size spheres were produced via the ultrasonic spray pyrolysis method using copper nitrate without any additives. The effects of the process temperature and solution concentration on the copper oxide particles were investigated. HSC software, differential scanning calorimetry and thermal gravimetric analysis were used for the thermodynamic investigation of the CuO formation by the decomposition reaction. Particle characterization studies were performed using X-ray diffraction, energy dispersive spectroscopy, scanning - and transmission - electron microscopy. The results show that spherical CuO nanoparticles having around 80 nm particle size were prepared at 400 degrees C and the submicron size CuO spheres were obtained by the aggregation of nanoparticles at elevated temperatures. The crystallite sizes of the particles ranged between 21 and 46 nm.