Purely siliceous MCM-41, MCM-48, SBA-15, and Ni-containing molecular sieves were synthesized by the sol–gel method. The impact of the Ni loaded by incorporation and impregnation in the framework of molecular sieves on the textural and morphological characteristics of the solids was comprehensively investigated. The incorporation method proved to be more effective in terms of textural and morphological properties; therefore, we also investigated the influence of Ni incorporation on the structure of MCM-41 at different loadings (3, 6 and 9 wt.%). Moreover, all solids were characterized by FT-IR, TGA, XRD, SEM-EDS, and N₂ adsorption. The resulting mesoporous materials exhibit a porous structure with well-defined pore sizes of about 2.0–5.0 nm and high specific surface areas (634 m²g⁻¹ for SBA-15, 1592 m²g⁻¹ for MCM-48, and 1769 m²g⁻¹ for MCM-41) alongside uniform pore size distributions. The MCM-41 structure remained unchanged after loading of Ni; however, its surface area and pore diameter decreased due to pore blockage.