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A large quantity of uniform ZnO nanoneedles has been synthesized by thermal evaporation method. Both single and double tip ZnO nanoneedles were found coexistence in the as-synthesized products. The single tip nanoneedles are major products in the synthesis and a few double tip nanoneedles were also observed. The polarity of the nanoneedles was characterized by convergent beam electron diffraction (CBED) and the simulation results reveal that the polarity of the ZnO (0001) surface directs the preferential growth of the nanoneedles. It is also found that most of the double tip nanoneedles are originated from the joint growth of two single tip nanoneedles with a kink in the middle and smooth ones might be generated from forming thin layer of cubic structures in the double nanoneedle tips. A large quantity of ZnO nanorod building blocks without tips was also achieved by fast cooling. The formation of the nanoneedles and nanorods can be attributed to different cooling speeds in our experiments. The sharp single nanoneedle tip can be potentially used as scanning probe microscope or field-emission tips.