A variety of hierarchical oxide nanostructures, including ZnO nanonails on nanowires/nanobelts, ZnO nanorods on nanobelts, comb-like ZnO nanostructures, hierarchical MgO nanowires, etc., have been synthesized by thermal vapor evaporation and condensation. Observation of these nanostructures demonstrates the diversity of the geometry of these oxides in the nanoscale range. These nanostructures may be helpful in studies of nanostructure growth mechanisms and may find applications in nanoelectronics, opto-electronics, catalysts, displays, etc.