In this study, hierarchically three-dimensional (3D) nanotubular sea urchin-shaped iron oxide nanostructures (3D-Fe2O3) were synthesized by a facile and rapid ultrasound irradiation method. Additives, templates, inert gas atmosphere, pH regulation, and other complicated procedures were not required. Dense 3D-Fe2O3 with a relatively large Brunauer-Emmett-Teller (BET) surface area of 129.4 m(2)/g was synthesized within 23 min, and the BET surface area was further improved to 282.7 m(2)/g by a post heat-treatment process. In addition, this post