Mesoporous silica membranes were prepared by solvent evaporation methods using tetraethyl orthosilicate (TEOS) as a silica source and hexadecyltrimethylammonium chloride (CTAC) as a template and applied to filtration membranes which enable to separate solutes by nano-order size. Effect of the membrane thickness on structure formation was studied. The final membrane thicknesses were controlled from 0.43 mu m to 127.7 mu m by several deposition methods, such as spin-coating, casting by applicator, and pouring in Petri dish. The mesophase of the membrane changed from a cubic phase to a one-dimensional hexagonal (1d-H) phase with increasing membrane thickness. The membrane thickness was one of the key factors to control the mesostructure formed in the solvent evaporation method. In the monitoring of the structural growth process, it was found that 1d-hexagonal structure was initially obtained on a glass substrate, and this structure was changed to cubic structure. This result can be explained by changing the surfactant concentration, which decides the mesostructures. For filtration application, the silica membrane with the cubic structure was deposited by spin-coating on the porous alumina substrate. The rejection coefficient of Vitamin B-12 with the molecular weight of 1355 was about 0.8. (C) 2005 Elsevier B.V. All rights reserved.