Perovskite-type LaMnO3 and La0.8Sr0.2MnO3 with high specific surface areas were prepared by stearic acid gel combustion method. The obtained powders were characterized by XRD, SEM and XPS techniques. Their catalytic activities were investigated on thermal decomposition of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by TG-DSC techniques. The experimental results show that LaMnO3 is a more effective catalyst than La0.8Sr0.2MnO3 for the sublimation and melting process of RDX because of its higher concentration ratio of surface-adsorbed species. And the catalytic activity of La0.8SrO2MnO3 is higher than that of LaMnO3 for thermal decomposition of liquid RDX. This could be attributed to its higher concentration ratios of surface oxygen and Mn4+/Mn3+. In conclusion, the concentration ratios of surface oxygen and Mn4+/Mn3+ could play key roles for RDX thermal decomposition. This study points out a potential way to develop new and more active perovskite-type catalysts for the RDX thermal decomposition. (C) 2009 Elsevier B.V. All rights reserved.