Industrial zeolitic membranes which offer a remarkable selectivity compared to polymeric membranes, suffer of the lower flux due of their larger thickness (e.g., 10-30 mu m). This problem can be addressed by controlled synthesis of nanolayers, resulting in thinner membrane layers (e.g., 0.5-5 mu m). An aluminosilicate gel with a molar composition of 20SiO(2):Al2O3:10K(2)O:400H(2)O was used to prepare several membranes of zeolite L by means of a controlled hydrothermal synthesis on the surface of a porous alumina disc seeded with nanozeolite LTL crystals. Nanocrystallites of LTL zeolite with an average particle size of 80-100 nm were successfully synthesized and characterized. Using these nanoparticles as seeds, a zeolite L layer with an average thickness of 2 mu m was synthesized on the alumina support at 150 degrees C.