Although hydrotalcite or layered double hydroxides (LDHs) is not a common mineral, it is an important material that can be easily synthesized in laboratory. In this study, structural evolution and BET surface area changes of heat treated Mg/Al-LDH was evaluated by XRD, TEM and N2-BET analyses. The results indicate that for magnesium-aluminum LDH with carbonate as interlayeranion, periclase-like oxide was formed at the temperature of 400～800℃. Meanwhile, 2-3 nanometer mesopores were formed during the decomposition of LDH. However, the heat treated samples still preserve the morphology of original LDH plates. Periclase-like oxide formed from LDH heat treatment may re-hydrolyze and recover the structure of LDH. However, crystallinity of the recovered LDH is lower than that of original LDH. Such a heat treatment will result in the formation of (Mg, Al)-oxide nano-crystals and nanopores among the nano-crystals. When the heating temperature exceeds 1 000℃, the periclase-like (Mg, Al)-oxide was transformed into a composite with periclase (MgO) and spinel phases. The periclase can be re-hydrolyzed and dissolved in HCl solution. After acid treatment, the sample with high surface area is composed of spinel nano-crystals and nanopores among them. The results of this study will provide a new and economical way to synthesize mesoporous materials through pathways of phase transformation of precursor materials with different compositions.