MnO_x/CeO₂-Al₂O₃ monolith catalysts were prepared by impregnation method. The catalysts were characterized by X-ray diffraction (XRD) and temperature-programmed reduction (TPR) methods, The H₂O₂ decomposition reaction activity was determined by oxygen-gasometry of the reaction kinetics in a constant pressure reactor. The stability of monolith catalysts for the decomposition of high concentration hydrogen peroxide was evaluated in a monopropellant thrust hot test system using 90% H₂O₂. The results show that CeO₂ can promote the interaction between MnO_x and CeO₂, the dispersion of Mn species, and the oxidation of low value Mn³⁺ to more active high value Mn⁴⁺, through the formation of surface active oxygen and Mn-Ce-O solid solution. The rise of more active Mn species of Mn⁴⁺ increases the number of low temperature active sites and the ability of reduction-oxidation of catalysts. MnO_x/CeO₂-Al₂O₃ monolith catalyst has a higher activity and stability for high concentration hydrogen peroxide decomposition reaction, compared to MnO_x/Al₂O₃ monolith catalyst.