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La₂O₃ doped alumina aerogels with different La₂O₃ contents are prepared by using aluminum tri-sec-butoxide as precursor via sol-gel route combined with acetone-aniline in situ water formation (ISWF) method, followed by supercritical fluid drying. The effect of La₂O₃ on microstructure and thermal stability of alumina aerogels is investigated by SEM, TEM, XRD and N₂ adsorption. The results show that the morphology of alumina aerogels changes from sphere like accumulated to notably sheet like stacked with the doping of La₂O₃. An appropriate amount of La₂O₃ doping can enhance the specific surface area of alumina aerogels, and the 9 mol% La₂O₃ doping aerogels has the largest specific surface area. In addition, the alumina crystal growth and phase transition of the aerogels upon heat treatment are effectively inhibited by La₂O₃ doping, which significantly improves the thermal stability of the aerogels. After heat treatment at 1200℃ for 2h, the phase of 9 mol% La₂O₃ doped alumina aerogel remains in the θ-Al₂O₃ while that of undoped one is a-Al₂O₃, and the specific surface area of 9 mol% La₂O₃ doped alumina aerogel is 86.5 m₂/g which is higher than the undoped one (46 m₂/g).