The activation energy for the thermal decompostion of chemical compounds can be determined using isothermal or nonisothermal TGA measurements or by using the recently introduced modulated TGA method (MTGA, TA Instruments). In the course of our investigation on the decompostion of complexes, we started a comparative study of different measurement and calculation procedures for the thermal decompositon of Mn(Urea)(2)Cl-2. As a reference, we did the same study on the sublimation of N-n-propyloxamide. The results of our comparative study on the determination of the activation energy for the decomposition/sublimation of these compounds are given.