To obtain the thermal decomposition characteristics of mononitrotoluene(MNT) with nitric-sulfuric mixed acid, differential scanning calorimeter(DSC) and accelerating rate calorimeter(ARC) were employed to test the thermal decomposition behaviors of pure MNT and its mixture with 5% and 79% nitric-sulfuric mixed acid.DSC results show that the mixed acid catalyzes the decomposition of MNT mixture.The more concentration the mixed acid, the lower initial decomposition temperature of MNT mixture.ARC results demonstrate that the initial decomposition temperature decreases from 260.7 ℃(MNT) to 150.7 ℃(MNT with 79% mixed acid), and the temperature at which the time to maximum rate is 24 h(T_D24) from 299 ℃ to 98 ℃.Meanwhile, both the heat of reaction and the adiabatic temperature rise of MNT mixture increase a bit.Thus, the mixed acid decreases the thermal stability of MNT mixture, and increases the thermal hazards.