Using 20 L spherical explosion vessel, the explosion characteristics of nano-aluminum powders with different sizes were investigated. Compared with micro-scale aluminum powders explosion, nano-powders explosion processes and mechanisms were analyzed based on the auxiliary analysis of scanning electron microscopy (SEM) and X-Ray diffraction (XRD). The results show that the maximum explosion pressure and maximum rate of pressure rise mainly depended on the dust concentrations. With the increasing of dust concentration, the maximum explosion pressure increases gradually to the maximum when the dust concentrations below 1000 g/m(3) and then the maximum explosion pressure decreased especially for the dust concentrations higher about 1250 g/m(3). At the same time, the trends of maximum rate of pressure rise performed the similar rules with the dust concentrations. For the selected nano-powders, particle size change seems no obvious explosion differences. However, for micro-sized aluminum powders, explosion characteristic presents decreased change rules with the particle size increase. At the same time, the lower explosion concentration limits of aluminum powders explosion were measured and presented. Research result may have important implications for nano-sized aluminum powders utilization and safety operation. (C) 2011 Elsevier B.V. All rights reserved.