Preparation, X-ray crystal structure, thermal behavior, and IR spectroscopic studies of cis-diaquabis(1,10-phenanthroline)zinc(II) diorotate hydrate are described. In the compound [Zn(H2O)2(C 12H8N2)2](C5H 3N2O4)2·(H2O) 2.125 (1), the zinc ion, located on a twofold axis, is coordinated by two aqua ligands together with a pair of bidentate 1,10-phenanthroline (phen) molecules, and exhibits a distorted octahedral coordination. The orotate anions have a single negative charge each. The metal-coordinated water molecules link the orotate ions to the metal complex via O-H⋯O hydrogen bonds. Also the uncoordinated water molecules are bonded to orotate ions through O-H⋯O hydrogen bonds. Thus, an extensive network of hydrogen bonds together with π-π, and π-ring interactions stabilize the crystal structure and form an infinitive three dimensional structure. The thermal decomposition pathway of 1 has been investigated by the help of thermal analysis data (TG, DTG and DTA). © 2006 Verlag der Zeitschrift für Naturforschung.