The particle size of primer mixture plays an important role on firing characteristic s of electro-explosive devices. In general. explosive was classified by the particle size. In this work, we found that the decomposition temperature of potassium perchlorate with a particle size smaller than 44 μm was higher than the particle size between 44 μm to 74 μm. The result was beyond our expectations. In order to explain the above result. we investigated the thermal behaviors of potassium perchlorate by thermal analysis technique.