Mn₃O₄ microspheres were successfully prepared by a solvothermal method using manganese (II) acetate tetrahydrate and anhydrous ethanol as raw materials. The effects of reaction temperature and reaction time on experimental results were investigated and discussed. The optimum conditions of reaction at 160 ℃ for 4 h were obtained. The composition and morphology of Mn₃O₄ microspheres were characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The effect of Mn₃O₄ microspheres on the thermal decomposition of ammonium perchlorate (AP) was investigated by differential scanning calorimeter (DSC). Results show that Mn₃O₄ microspheres are an aggregation of ultrafine Mn₃O₄ particle with high crystallinity and a size of 4-10 nm. In comparison with pure AP, the decomposition peak temperature of AP in Mn₃O₄ microspheres/AP mixture shifts by 160.1 ℃ downwards, and appears at 297.1 ℃, indicating that Mn₃O₄ microspheres have a significant catalytic effect on thermal decomposition of AP.