Mesostructured lamellar, hexagonal and cubic vanadium-phosphorus-oxide (VPO) phases were prepared employing cationic, anionic and alkylamine surfactants under mild conditions and low pH. The obtained mesophases displayed desirable vanadium oxidation states (+3.8 to +4.3) and P/V molar ratios similar to1.0 for the partial oxidation of n-butane to maleic anhydride. As-synthesized mesostructured VPO underwent phase transformations to various mesostructured and dense VPO phases depending on the post-synthesis treatment. The phase transformations of mesostructured VPO during Soxhlet extraction and thermal treatment in N-2 have been observed for the first time. These transformations were explained by the changes in the surfactant packing parameter, g. Calcination in air produced more disordered mesostructures and dense VPO phases such as gamma-VOPO4 and (VO)(2)P2O7.