An ultrasonically assisted two-step polyol process was established to fabricate polycrystalline ZnO nanotubes. Thus one-dimensional (1D) precursors were prepared from an ethylene glycol (EG) solution containing 0.3 M of zinc acetate in the presence of ultrasonic irradiation. The ZnO nanotubes were obtained by calcination of the precursors at proper temperatures. The precursors and polycrystalline ZnO nanotubes obtained at various calcination temperatures were characterized by means of scanning electron microscopy (SEM), Fourier transformation infrared spectrometry (FTIR), x-ray diffraction (XRD, together with temperature-resolved XRD), and transmission electron microscopy (TEM). It was found that the precursors were extremely sensitive to atmospheric moisture and instantly transformed to layered hydroxide zinc acetate (LHS-Zn) after being exposed to air, accompanied by the erosion and deformation of the one-dimensional structure. After being calcined at proper temperatures, the precursors were completely transformed into polycrystalline tubular ZnO, and the sizes of the resulting ZnO nanocrystallites increased with increasing calcination temperature, implying that polycrystalline tubular ZnO of desired sizes could be fabricated using the present method by properly controlling the calcination temperature. However, the tubular structures were destroyed at a calcination temperature of 400 °C and above, owing to the growth of polycrystalline ZnO. Moreover, the present method could be used to synthesize other tubular metal oxides, and tubular ZnO might find promising applications in gas-sensitive sensors and catalysis as well.