The thermal decompositions of Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of saccharin were studied in static air atmosphere. All of the complexes contain four molecules of coordination water and two molecules of crystallization water. The water molecules were removed in a single stage, except from the Zn(II) complex, which exhibited two endothermic effects. The dehydration process was usually accompanied by a sharp colour change. The anhydrous complexes exhibited a phase transition and the decomposition or combustion of saccharin occurred in the second and subsequent stages. The final decomposition products were identified by XRPD as the respective metal oxides. The kinetic parameters, such as the order of reaction and energy of activation for the dehydration stage, were evaluated and the thermal stabilities of the complexes are discussed.