Six-prism ZnO microtubes and three-dimensional (3D) microflowers were successfully synthesized using methenamine and zinc nitrate as precursors in an aqueous solution. The as-synthesized microtubes have an average diameter of about 1 mu m and length of 7-8 mu m. The as-synthesized microflowers comprise six-prism microrods with an average diameter of about 300-400 nm and length of 1-2 mu m. The microrod arrays radiate outwards. The structure and composition of the samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), UV-vis diffusive reflectance spectroscopy, and photoluminescence (PL) spectroscopy. The effects of heating temperature and time on the morphologies and orientations of the ZnO microstructures were experimentally studied. The formation mechanism is discussed in detail. (C) 2012 Elsevier B.V. All rights reserved.