The thermal dissociation of complexes formed by copper(II) chloride with photoproducts of M(CN)(8)(4-) [where M=Mo or W] and ethylenediamine has been studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and IR spectroscopy. The observed IR bands for different groups support the assigned composition. Both Mo(IV) and W(IV) show the same stoichiometric behaviour towards complex formation but a different decomposition behaviour. In case of Mo(IV) decomposition takes place in four steps with cyanide and oxide of copper and tetrachloro molybdenum(IV) as residue, while in case of W(IV) the decomposition occurs only in three steps up to 298 degrees C. The copper cyanide along with tetrachloro tungstate(IV) is found as residue. DSC for Mo complex displays four transitions, two exothermic and two endothermic. In case of W, DSC displays three endothermic transitions corresponding to three decomposition steps with three different Delta H values. On the basis of TG and DSC, mechanism for decomposition of each complex has been proposed. Kinetic parameters like activation energy (E-a), frequency factor (A), entropy of activation (Delta S-#) for each step has been calculated involving differential methods like Doyle, Coats and Redfern and Arrhenius. The heat of the reaction is obtained from DSC curves.