The influence of the particle size on the thermal decomposition of epsilon-hexanitrohexaazaisowurtzitane (HNIW) was studied hy means of differential scanning calorimetry (DSC), The kinetics and mechanism for the decomposition were evaluated using integral methods. It was found that the thermal kinetic parameters such as activation energy (E) and pre-exponential factor (A) depend little on the particle size of epsilon-HNIW in the range 4-180 mu m, and an A3 model function fits most of the data from the decomposition of the material.