Aluminum hydroxide gels were prepared by the sol-gel method. The role of acid in sols was investigated through the analysis of gelling time and hydrolysis rate. The phase transformation of gels with calcination temperatures was also monitored with X-Ray diffraction. The gelling times of the aluminum hydroxide sols decreased with the increase of acid content. Exceptionally, the solution peptized with 0.07 HCl/ alkoxide molar ratio look longer time than other solutions until the gellation. The hydrolysis rate of aluminum hydroxide was much faster as the acid concentration increased during peptization. In the case of NH₄OH as a peptizing agent, there was the lower rate of hydrolysis and thus the more alkyl groups were remained in the gel.

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