Size effect and photocatalytic activity of CuO sheet-like nanostructures, which were synthesized by a facile solution phase chemical method with ethanol and water mixture as solvent, have been investigated by UV-vis absorption spectrum and photocatalytic degradation of pollutant rhodamine B (RhB). UV-vis absorption spectrum indicated that the band gap energy was about 2.31 eV for the as-prepared CuO nanostructures. The result indicates that the band gap energy of the CuO sheet-like nanostructures is much larger than value of bulk CuO crystals, showing that the CuO sheet-like nanostructures exhibit a strong quantum size confinement effect. The photocatalytic activity indicates that the as-synthesized CuO sheet-like nanostructures show an enhanced photocatalytic activity with 96.7% degradation of RhB after 9 h reaction under UV light irradiation, which was much higher than that of commercial CuO powders (39.6%). (C) 2013 Elsevier B.V. All rights reserved.