Recent advances in the synthesis of hydrothermally stable mesoporous aluminosilicates (MAs) by assembling precursors shed light on their applications in residue fluid catalytic cracking. Reducing the n(H2O)/n(SiO2) ratio and thus reducing waste discharge is the key for practical applications of MAs. In this study, the synthesis of hydrothermally stable MAs with a decreased n(H2O)/n(SiO2) ratio has been developed based on seed-assisted crystallization. Crystal seeds were partly dissolved to microcrystallites on which a large amount of zeolite precursors are assembled and crystallized. As a direct result of the assembly priority of crystal seeds, the concentration and viscosity of the liquid phase in the synthesis system will be decreased greatly. Afterward, the remaining precursors with proper concentration and viscosity can be assembled with the surfactant micelles. Therefore, the H2O amount could be largely decreased by the introduction of crystal seeds.