In this study, we found that ammonium-functionalized polyhedral oligomeric silsesquioxanes (POSSs; 2Am-POSS and Am-POSS) with high proportions of cagelike decamer (T10-POSS; 54% and 45%, estimated from 29Si NMR spectra) could be successfully prepared by the hydrolytic condensation of 3-(2-aminoethylamino)propyltrimethoxysilane and 3-amimopropyltrimethoxysilane, respectively, using trifluoromethanesulfonic acid as a catalyst in hydrophobic alcohols such as 1-hexanol. In addition, on the one hand, it was also found that 2Am-POSS, a mixture of cagelike octamer (T8-POSS), T10-POSS, and cagelike dodecamer (T12-POSS), could be separated into T8-POSS and a mixture of T10- and T12-POSSs by exploiting their different solubilities in 1-butanol. On the other hand, in the case of Am-POSS, T8-POSS and a mixture of T10- and T12-POSSs could be isolated by treatment with ethanol-methanol mixed solvent and 1-propanol. The XRD patterns of cast films of T8-POSS showed many sharp diffraction peaks, indicating crystalline structures, whereas those of T10- and T12-POSSs showed no diffraction peaks, indicating amorphous structures, for both the case of 2Am-POSS and Am-POSS. These results suggest that the difference in crystallinities between the ammonium-functionalized T8-POSS and T10- and T12-POSSs causes their different solubilities in alcohol solvents.