The complex of [Sm(p-MOBA)3phen]2 (p-MOBA, p-methoxybenzoate; phen, 1,10-phenanthroline) was prepared and characterized by elemental analysis, IR, and UV spectroscopy. The thermal decomposition of the [Sm(p-MOBA)3phen]2 complex and its kinetics were studied under a static air atmosphere by TG-DTG methods. The intermediate and residue for each decomposition stage were identified from the TG curve. The kinetic parameters and mechanisms of the first decomposition stage were obtained from the analysis of the TG-DTG curves by a new method of processing the data of thermal analysis kinetics. The lifetime equation at a mass loss of 10% was deduced as lnτ= - 30.6795 +21034.56/T by isothermal thermogravimetric analysis.