[Co(Et XA) 2·phen]·H 2O was prepared by adding 1,10 phen~anthroline to the EtOH solution of bis( O ethylcarbo~no~di~thio~lato)cobalt(II) [Co(Et XA) 2]. The single crystal structure has been determined by X ray diffraction analysis. The compound is orthorhombic with space group Pna 2 1 and unit cell parameters a =1 0290(2) nm, b =1 4550(3) nm and c =1 4860(3) nm. The geometry of each Co atom which coordinates with four S atoms from two xanthate anions and two N atoms from phenanthroline ligand, is a distorted octahedron. The brown crystals were examined by elemental analysis, FT IR, UV spectra and thermogravimetric differential thermal analysis (TG DTA). Thermal decomposition of the compound takes place in several steps. In the first step, the compound releases 1,10 phenanthroline ligand, then loses the H 2O molecules. In the second step, the complex decomposes to CoS 3. The final product of thermal decomposition is CoS. Elemental analysis, IR and UV spectra are in agreement with the proposd structure. [Co (Et XA) 2 · phen] · H 2 O was prepared by adding 1,10 phen- anthroline to the EtOH solution of bis (O ethylcarbo ~ no ~ di ~ thio ~ lato) cobalt ) 2]. The single crystal structure has been determined by X ray diffraction analysis. The compound is orthorhombic with space group Pna 2 1 and unit cell parameters a = 1 0290 (2) nm, b = 1 4550 (3) nm and c = 1 4860 (3) nm. The geometry of each Co atom which coordinates with four S atoms from two xanthate anions and two N atoms from phenanthroline ligand, is a distorted octahedron. The brown crystals were examined by elemental analysis, FT IR, UV spectra and thermogravimetric differential thermal analysis (TG DTA). Thermal decomposition of the compound takes place in several steps. In the first step, the compound releases 1,10 phenanthroline ligand, then loses the H 2O molecules. In the second step, the complex decomposes to CoS 3. The final product of thermal decomposition is CoS. Elemental analysis, IR and UV spectra are in agreement with the proposd structure.