Hexagonal crown-capped ZnO micro rods were successfully prepared by a facile low-temperature hydrothermal method. The as-prepared ZnO micro rods are 4.4-5.2 mu m in length and 2.4-3.6 mu m in diameter, possessing a single crystal hexagonal structure. The morphology evolution and structure changes were tracked during,hydrothermal growth by field. emission scanning electron microscopy and X-ray diffraction, respectively. A three-stage growth mechanism of the hexagonal :crown-capped ZnO micro rods was proposed and further verified by a growth solution renewal experiment. The room-temperature photoluminescence (PL) spectrum of the hexagonal crowns exhibits a strong UV emission at about 382 nm. The temperature dependent PL results indicate that the UV emission originates from the radiative free-exciton recombination.