Abstract: The thermal decomposition reaction of 3,6-diphenyl-1,2,4,5-tetroxane (DFT), within the temperature range of 130.0-150.0°C and initial concentrations equal to 1.69x10-3 mol L-1 with addition of the copper-compound CuCl2 (4.0x10-4 M) has been studied in methanol solution. The thermolysis follows a first-order kinetic law up to ca 60% DFT conversion. Under the experimental conditions, the activation parameters of the initial step of the reaction (ΔH# = 19.0±0.8 kcal mol-1; ΔS# = -20.1±1.8 mol-1 K-1; ΔG# = 27.3±0.8 kcal mol-1) and benzaldehyde, as the organic product, supports a stepwise reaction mechanism with the homolytic rupture of one of its peroxidic bonds. Also, the participation of cupric ions in the reaction is postulated to give an intermediate diradical, which further decomposes by CO bond ruptures, yielding a stoichiometric amount of benzaldehyde. The results are compared with those obtained for the above diperoxide thermolysis in methanol whitout the presence of the copper-compound.