Abstract: Mercury (II) complexes of reduced glutathione (GSH) of general composition [Hg(L)(X)]H2O (where HL = GSH; X = NO3−, SCN−, CH3CO2−, Cl−) have been synthesized and characterized by elemental analysis, infrared spectra and electronic spectral studies. The stability constant of the mercury complex has been evaluated potentiometrically, and thermogravimetric (TG) and differential thermal analytical (DTA) studies have also been carried out for these complexes. Infrared spectra indicate deprotonation and coordination of cysteinyl sulfur with the metal ions. It indicates the presence of water molecules in all the complexes which has been supported by TG and DTA studies. The thermal behavior of complexes shows that the water molecule is removed in first step, followed by the removal of anions and then decomposition of the ligand molecule in subsequent steps. General mechanisms describing the decomposition of the solid complexes are suggested. Kinetic and thermodynamic parameters were computed from the thermal decomposition data. The geometry of the metal complexes has been optimized with the help of molecular modeling.