Al2O3 gel was prepared by hydrolysis of aluminum alkoxide. The prepared Al2O3 gel powder was calcineel at the various temperature in the electric furnace. To investigate thetransition of crystals thermal properties X-ray diffractometry SEM specific surface area by BET nitrogen adsorption FT-IR and TG-DTA technique were employed. Transparent alumina gel was opalized at 120$0^{circ}C$ The alumina gel was transformed along the rising of temperature as follows ; Boehmite (AlOOH) longrightarrow$sigma$-Al2O3longrightarrow$alpha$-Al2O3