The synthesis, characterization and thermal degradation study of gadolinium and lutetium methanesulfonates is reported. The prepared salts were characterized by elemental analysis and infrared spectroscopy. The thermal degradation study was performed by using thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). By using thermogravimetric data, a kinetic study of the dehydration of Gd and Lu methanesulfonates is performed employing the Coats-Redfern and Zsako methods. It is verified that under heating, the gadolinium and lutetium methanesulfonates suffer three main processes: dehydration, thermal degradation and oxide formation. The thermal degradation products were characterized by infrared spectroscopy and X-diffractometry. Furthermore, depending on the atmosphere nature, i.e. inert or oxidant, the thermal degradation process could be endothermic (N-2) or exothermic (air). (C) 2004 Elsevier B.V. All rights reserved.