Supported type 1 bicontinuous cubic (Q(1)) lyotropic liquid crystal (LLC) polymer membranes with a 3D-interconnected porous structure and an effective pore size of 0.75 nm were modified by alumina atomic layer deposition (ALD). The ALD-modified polymer membranes have an effective pore size smaller than 0.55 nm and show promise for gas separations. With 10 cycles of alumina ALD coating, the selectivity of an ALD-modified Q(1)-phase LLC polymer membrane for H(2)/N(2) greatly increased from 12 to 65, while the permeance of H(2) decreased similar to 40%. The ALD membrane modification approach described here appears to be universal and has the potential to modify other nanoporous membranes for size-selective separation. (C) 2009 Elsevier B.V. All rights reserved.