In this paper, ZnO microflowers were synthesized on silicon substrates by the thermal oxidation of pure Zn powder(99.99%). The X-ray diffraction spectrum (XRD) showed that ZnO microflowers have a hexagonal wurtzite structure. The field-emission scanning electron microscope (FE-SEM) image indicated that as-synthesized ZnO microflowers consisted of lots of long and straight microrods, which possessed hexagonal prism morphology. The length of microrods ranges from 30 to 50μm. The resonant Raman spectrum showed multiphonon scattering process the 5th-order longitudinal optical phonon (A1(LO)) mode in the backscattering geometry, indicating that the sample is of high quality. In the temperature-dependent photoluminescence (PL) spectra, “ negative thermal quenching” phenomenon of neutral acceptor bound exciton (A0X) was observed, and its origin was discussed.