Abstract: Carbon nanoonions were synthesized by arcdischarge with graphite electrodes submerged in water. The products were characterized by Raman spectroscopy and highresolution transmission electron microscopy. It was found that the density of the arcdischarge current had a significant influence on the morphologies and the output of the products, which aggregated near the surface of the water or precipitated on the bottom. When the current used was about 40A, the products collected near the surface of the water were wellcrystallized spherical carbon nanoonions, 520nm in diameter, and the output capacity was about 4.3mg/min, indicating that a large amount of high quality nanocarbononions could be prepared by this technique.