Three kinds of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) samples with spherical (beta-phase), needle (gamma-phase) and polyhedral (beta-phase) shapes were fabricated by wet milling, solvent/non-solvent and riddling methods, respectively. By changing the technical conditions, HMX powders with different particle sizes were obtained for each kind of sample. All as-prepared samples were characterized by laser granularity measurement, scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Taking advantage of mechanical sensitivity tests, slow cook-off tests and differential scanning calorimetry (DSC) analysis, the mechanical sensitivity and thermal stability of HMX samples were found to depend on particle size and morphology. Results indicated that particle size played a significant role in the safety of HMX, and that morphology regulated the experimental results, i.e., for each kind of HMX samples, the mechanical sensitivity and thermal stability of HMX changed if the particle size differed. However, the trends of these changes exhibit much variance if the microstructure of the HMX particles is altered. Consequently, the difference in safety for these kinds of samples has to do with their specific morphology. (c) 2008 Elsevier B.V. All rights reserved.