Highly selective membranes with controlled porosity can be obtained by growing thin films of mesoporous oxides on an appropriate support. This can be achieved employing organic/inorganic mixed micellar solutions based on metal oxide precursors and commercial templates. In particular amphiphilic block copolymers are very attractive materials as soft-templating agents because they self-assemble into micelles whose morphology and size depend on block composition and solution parameters. Large-mesopore silica films with narrow pore size distribution and high porosity have been obtained by sol-gel reaction of a silicon oxide precursor (TEOS) and using polystyrene-block-poly(ethylene-oxide) (PS-b-PEO) copolymers as templates. In order to modulate size, shape and alignment of the pores, many variables were changed: block copolymer chain length, TEOS/block copolymer ratio, solvent ratio, additives (i.e. polystyrene homopolymer addition). The effect of the different parameters on the porous system was studied by microscopy techniques and gas-volumetric analyses. Final aim of this work is the preparation of silica membranes to be used as selective gates for controlled dosing and transport of chemical species in solution