Copper oxide (CuO) nanoparticles are synthesized by aqueous precipitation method using copper acetate as a precursor and NaOH as a stabilizing agent. This gives a large scale production of CuO nanoparticles easily. X-ray diffraction pattern (XRD) reveals single phase monoclinic structure. Scanning electron microscopy (SEM) showed the rectangular morphology of as prepared CuO nanoparticles. The transmission electron microscopy (TEM) showed 5-6 nm size of as prepared CuO nanoparticles. Photoluminescence (PL) showed band edge emission at 398 nm and green emission at 527 nm. The band edge-absorption peak is found to be at 355 nm.