Controlled synthesis of ZnO nanorods (ZNRDs), nanotubes (ZNTs) and nanorings (ZNRs) has been carried out by a two-step sonochemical/chemical process at room temperature without any catalyst, template or seed layer. The crystallinity, structure and morphology of ZNRDs, ZNRs and ZNTs were examined by X-ray diffraction (XRD) analysis, scanning electron micrographs (SEM), high resolution transmission electron microscope (HR-TEM) and selected area electron diffraction (SAED). The as-prepared ZnO nanostructures were single crystalline with hexagonal cross-section and uniform size. The effect of precursor concentration on the growth and that of the etching duration on the hollow formation were analyzed, and the obtained results revealed that the precursor concentration and etching time play an important role in determining final morphologies of the samples. By tuning the etching time, the precise size control of ZNTs and ZNRs was achieved. Possible formation mechanisms of these nanostructures are proposed based on the experimental results.