Alumina hydrates were prepared by the neutralization of AlCl3.6H2O solution with NH3 gas diluted with N2 gas. The values of pH in reaction solution influenced the formation of alumina hydrates minerals. Amorphous alumina hydrates, for example, were formed at <pH 8.2, pseudo-boehmite at pH 8.2 up to pH 9.30 and bayerite at pH 9.30<, respectively. And they were transformed with increasing temperature, as follows. (1) Pseudoboehmitelongrightarrowamorphouslongrightarrow${gamma}$-Al2O3longrightarrow$delta$-Al2O3longrightarrow$ heta$-Al2O3longrightarrow$alpha$-Al2O3. (2) Bayeritelongrightarrowamorphouslongrightarrow${gamma}$-Al2O3longrightarrow$delta$-Al2O3longrightarrowη-Al2O3longrightarrow$ heta$-Al2O3longrightarrow$alpha$-Al2O3. On the other hand, the shape of alumina hydrates whichw ere prepared by the reacton of Al2(SO4)3.16H2O solution and NH3 gas was spherical, the progress of its phase transformation with increasing temperature was amorphouslongrightarrow${gamma}$-Al2O3longrightarrow$alpha$Al2O3 in sequence.