The tremendous potential of zeolite membranes for efficient molecular separation via size-exclusion effects is highly desired by the energy and chemical industries, but its practical realization has been hindered by nonselective permeation through intercrystalline spaces and high resistance to intracrystalline diffusion in the conventional zeolite membranes of randomly oriented polycrystalline structures. Here, we report the synthesis of ZSM-5 zeolite nanosheets with very large aspect ratios and nanometer-scale thickness in the preferred straight channel direction. We used these ZSM-5 nanosheets to fabricate ultrathin (<500 nm) laminated membranes on macroporous alumina substrates by a simple dip-coating process and subsequent consolidation via vapor-phase crystallization. This ultrathin b-oriented ZSM-5 membrane has demonstrated extraordinary water flux combined with high salt rejection in pervaporation desalination for brines containing up to 24 weight % of dissolved NaCl. The ZSM-5 nanosheets may also offer opportunities to developing high-performance battery ion separators, catalysts, adsorbents, and thin-film sensors.