Enormous absence of knowledge regarding dust explosion involving Engineered Nanomaterials (ENMs) has led to the exploration on investigating the Minimum Ignition Energy (MIE) of selected ranges of sizes for aluminum nanopowders. Nano-structure owned by alumina definitely contributes to changes in its chemical as well as physical composition. Thus, testing on MIE determination was conducted on three different particle sizes of aluminum nanopowders; A1-100nm, Al-70nm, Al-40nm. The main aim of the project is to determine the relationship of the particle diameter with their respective MIE. The overall experimental procedure take place using 1.2L Hartmann tube explosion system based on ASTM E2019. Two different dust concentrations were tested (250 g/m3 and 500 g/m3) and the results showed that Al-40 nm have the lowest MIE values of less than 5 mJ for both concentrations. For Al-70nm, the MIE value at concentration equals to 250g/m3 is between 10 mJ and 33 mJ, whereas the MIE is less than 10 mJ at concentration equals to 500 g/m3. This contradicts with Al-100nm in which the MIE is between 100 mJ and 200 mJ (c=250 g/m3) and between 33 mJ and 51 mJ (c=500 g/m3). In overall, as particle size decreasing, the MIE is significantly decreasing at respective concentrations. © Universiti Malaysia Pahang, Malaysia.