The suppression effects of ABC powder on 100 nm polymethyl methacrylate (PMMA) dust explosions with different mass densities were experimentally studied. Results showed that the suppressed flames were dim and the flame propagation was slowed down with the addition of ABC powder. When the proportion of suppressant increased, the average propagation velocity was decreased. After adding 30% ABC powder to 650 g/m(3) PMMA dust cloud, the maximum suppression ratio for velocity was 93%. After adding 10% ABC powder, the temperatures of PMMA dust cloud with the mass densities of 250 g/m(3), 450 g/m(3) and 650 g/m(3) were decreased to 19.8%, 27.4% and 33.1%, respectively. Meanwhile, the critical suppression proportion of PMMA dust explosion with three mass densities were 25%, 35% and 35%. Thermal analysis results showed that the addition of suppressant could increase the thermal stability of PMMA. The suppression mechanisms were comprised of physical suppression and chemical suppression which reflected on the consumption of H and OH radicals. The chemical kinetic models indicated that PO2 and HOPO played a catalytic role in the combination of H and OH. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.