The aluminum phthalate [Al4(OH)8(BDC)2]·H2O (where BDC2– stands for phthalate, i.e. 1,2-benzenedicarboxylate) denoted as CAU-15 (where CAU stands for Christian-Albrechts Universität) was synthesized under solvothermal conditions and thoroughly characterized. The structure was determined from X-ray powder diffraction data using a combination of direct methods and force-field calculations followed by subsequent refinement by Rietveld methods. The compound is built up by the interconnection of chains of edge-sharing AlO6 octahedra via phthalate anions, which results in a layered structure. Water molecules could be located between these layers and the dehydration behavior of the compound was studied by means of thermogravimetry and IR spectroscopy.