In the previous study(1), we showed that the microstructure of γ-AlO(OH) and γ-Al ₂O₃ particles was affected by aging stage in the γ-AlO (OH) sol preparation process. We investigated the effects of peptization as a continuous process after aging in γ-AlO(OH) sol preparation process on characterization of γ-Al ₂O₃ particles in this study. From the results, we found that there was no crystallinity and microstructure changes of γ-Al ₂O₃ particles as well as γ-AlO(OH) particles according to peptization. But there was a decrease of average pore diameter in γ-AlO(OH) particles at the beginning of the peptization. It shows that the adsorbed H₂O molecules on agglomerated γ-AlO(OH) particles were replaced by H₃ O⁺ of added peptization agent and then γ-AlO(OH) particles were repulsed against each other. As the result, the macropores within γ-AlO(OH) particles disappeared. Here, the peptization phenomenon occurred since agglomerated particles binded hydrogen bonds and olation bonds have been broken their bonds by the added H₃O⁺, there was happened to be peptization phenomenon. In summary, we concluded that microstructure of γ-Al₂O₃, particles was controlled by aging stage in sol preparation process and peptization was the process of finely suspended γγ-AlO(OH) sol preparation.