The mer-bis(2-aminothiazole)diaqua-orotato-nickel(II) complex, mer-[Ni(HOr)(H2O)(2)(ata)(2)] (1), was synthesized and characterized by spectral (IR and UV/vis) and thermal studies. In addition, the crystal structure of the complex was determined by single crystal X-ray diffraction. The complex crystallizes in the triclinic system, space group P1. The orotate ligand is coordinated to the nickel(II) atom through a nitrogen atom of the pyrimidine ring and an oxygen atom of the carboxylate group as a bidentate dianion. The coordination of the Ni(II) ion is extended to six by the two 2-aminothiazoles (ata) and two water molecules. The thermal decomposition has been studied in a static air atmosphere.