Alumina materials with ordered mesostructure and hierarchical porosity have been synthesized via a one-step process using aluminum iso-propoxide as an inorganic precursor, pluronic P123 as a template, hydrochloric acid and citric acid as the pH adjustors, and 1,3,5-trimethylbenzene (TMB) as a swelling agent. These mesoporous aluminas have relatively high surface areas (up to 309 m2/g), pore volumes (∼0.51 cm3/g), large pore sizes (up to 7.5 nm), and high thermal stability (up to 900 °C). In addition, the weight ratios of TMB/P123 play an important role in the synthesis process for controlling the mesostructures and pore sizes of the materials. The alumina with highly ordered 2-D hexagonal mesostructure (space group p6mm) can be synthesized with the weight ratios of TMB/P123 ranging from 0 to 3. Simultaneously, the pore sizes of ordered mesoporous aluminas were gradually enlarged with the increase of the TMB content. However, phase transformation of the mesoporous alumina from the 2-D hexagonal to hierarchical could be realized when the TMB/P123 weight ratio was increased to 5.