In order to investigate the catalytic activity of nano-MnO2 on the thermal decomposition of ammonium perchlorate, two different shapes of nano-MnO2 (sea-urchin and linear) were prepared by the hydrothermal method with MnSO4 center dot H2O and Na2S2O8, MnSO4 center dot H2O and (NH4)(2)S2O8, respectively. X-ray diffraction, scanning electron microscopy and the nitrogen adsorption/desorption analysis were used to characterize the structure of the nanocomposites. The sea-urchin nano-MnO2 possesses a greater specific surface area than the linear nano-MnO2. The catalytic properties of nano-MnO2 on the thermal decomposition of ammonium perchlorate (AP) were demonstrated by differential scanning calorimeter (DSC). As show in the DSC carves, the addition of the sea-urchin nano-MnO2 got the thermal decomposition peak temperature of AP reduced much more than the addition of the linear nano-MnO2, the low-temperature decomposition process even disappeared, and the high-temperature pyrolysis peak temperature decreased by 94.6 degrees C. All evidences indicated that the sea-urchin nano-MnO2 is a better catalytic than the linear one.