The crystal structure of two tubular zeolite Na-LTA membranes-one as-prepared membrane and a membrane used in vapor permeation (VP) processes of bioethanol-was analyzed using Rietveld refinement with parallel-beam powder X-ray diffraction data. The crystal structure of the as-prepared membrane was consistent with that of typical Na-LTA powder. After the VP process, an unusual relative peak intensity ratio between 200 and 220 reflections was observed in the membrane. The number of adsorbed water molecules in the beta-cage was reduced to half. Furthermore, detachment of sodium cations at the six-membered rings was confirmed. The electron density distributions of these Na-LTA zeolite membranes were analyzed by combining the Rietveld method and the maximum entropy method (MEM). MEM electron density images revealed that the adsorbed water molecules and Na+ cations were bonded, forming a hydrated cluster, and that the guest atoms or molecules were highly disordered.