Self-standing mesoporous membranes are prepared by full infiltration of ordered mesoporous silica precursors into textural macrospaces of frequently used cellulose membrane filters. We succeed in fabricating composite membranes that hardly contained large cracks/voids under the optimized conditions, realizing highly size-selective rapid transportation of biomolecules by their uniformity. Biomolecules with different sizes are precisely separated at the nanometer-level by using the mesoporous membranes.