Abstract: Filter cake, hydrated alumina and alumina prepared by aluminium sulphate-sodium aluminate method are hydrothermal treated by ammonium bicarbonate solution. The effects of NH₄HCO₃ hydrothermal treatment on the pore structure and surface properties of alumina are analyzed by XRD, FT-IR, SEM, N₂ adsorption-desorption, pyridine adsorption-desorption techniques respectively. It is found that NH₄HCO₃ hydrothermal treatment can increase the most probable pore of alumina, and decrease the total acid content, weak acid content and medium strong acid content, and also change the structure of surface hydroxyl. Compared with untreated alumina, the most probable pore of the alumina prepared from filter cake hydrothermal treated by NH₄HCO₃ is increased from about 5 nm to 8 nm, pore volume and surface area decreased slightly, total acid content decreased from 0.47 mmol/g to 0.30 mmol/g. Micron rod-like alumina is formed when different stage materials hydrothermal treated by NH₄HCO₃ solution. Pore structure and surface properties of alumina are affected by the formation of micron rod-like alumina.