An LEV-type aluminosilicate zeolite RUB-50 was synthesized in the presence of diethyldimethylammonium (DEDMA) cation as a structure-directing agent (SDA), and its crystal structure was analyzed in detail by the Rietveld refinement and the maximum entropy method (MEM). RUB-50 was crystallized from an Al-containing mother gel with relatively low water content. As-made RUB-50 contained a large amount of organic SDAs in the cavity, and therefore calcined RUB-50 exhibited a large micropore volume. Through the MEM analysis of the as-made RUB-50, the actual conformation of the SDA molecule occluded in the cavity emerged. In accordance with the structural analysis, quaternary ammonium cations possibly having molecular conformations similar to that of DEDMA successfully direct the crystallization of LEV-type zeolites. © 2009 Elsevier Inc. All rights reserved.