A process for preparing a mesoporous alumina is described, comprising the following steps: a) mixing, in aqueous solution, at least one source of aluminum constituted by an aluminum alkoxide, at least one cationic surfactant and at least one organic solvent selected from methanol and ethanol; b) hydrothermally treating the mixture formed in said step a); c) drying the solid formed in said step b); d) calcining the solid formed in said step c).