CuO microflowers composed of nanosheets, with tunable size have been fabricated through a simple reaction in ammonia solution at 90-180 degrees C, in which the nanosheets with zigzag edges were 20-40 nm in thickness and 500-800 nm in width. The high ammonia concentration, high ratio Of C-NH3 to C-Cu(2+) (R-ac) and elevated temperature were necessary for the formation of microflowers, and the ammonia concentration was critical for the morphology evolution of the particles. The fabrication mechanism of CuO microflowers based on the assembly of Cu(OH)(2) nanobelts was discussed. In addition, the CuO microflowers showed effective catalytic activity on the decomposition of ammonium perchlorate. (C) 2006 Elsevier Ltd. All rights reserved.