Abstract: The AlOOH nanorods and nanoflakes were prepared via hydrothermal synthesis using AlCl3?6H2O and NaOH. They were further converted into Al2O3 with same shape after calcination. Several techniques such as X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Fourier-transform infrared (FTIR) measurements were used to characterize the products. The results show that the products are γ-AlOOH. They were converted into γ-Al2O3 after calcinations. All the nanocrystals are single crystal with high crystallinity. The ratio of n（OH-）/n（Al3+） has a great influence on the shape of AlOOH and Al2O3. With the n（OH-）/n（Al3+）increasing, the ratio of length to diameter decreases for AlOOH which finally become nanoflakes. There are two types of OH groups on γ-Al2O3 nanorod, i.e HO-μ2-AlⅥ of Al2O3 (110) crystal plane and HO-μ2-AlⅥ of Al2O3 (100) crystal plane, respectively; There are four types of OH groups on γ-Al2O3 nanoflake. They are HO-μ3-AlⅥ and HO-μ2-AlⅥ of Al2O3 (111) crystal plane and HO-μ2-AlⅥ and HO-μ3-AlⅥ of Al2O3 (110) crystal plane.