Abstract: Hierarchically porous alumina with three-dimensional interconnected pore structure was prepared by phase separation method with alumina sol as the seed crystals; the alumina material was then characterized by SEM, XRD, N₂ sorption, mercury porosimetry and NMR. The results reveal that the ierarchically porous alumina is provided with macropores of 200-600 nm in gamma phase; it has a high surface area of 366 m²/g and narrow double pore size distributions at about 5 and 400 nm. As revealed by NMR, AlO₄, and AlO₆ are formed in the calcined alumina sample. It is then suggested that during the synthesis, PEO acted as a seed can inspire phase separation, generating the interconnected three-dimensional macropores, while the crystalline grain in the sol may induce the aluminum hydrates to form active AlOOH, which is then transformed to gamma crystalline phase by calcination even at mild temperature.