Poly(methyl methacrylate) (PMMA) and multi-walled nanotube (MWNT)/PMMA composites were irradiated in air. The constant dose rate was 985 rad/min at a dose of 5.7 Mrad using a Cesium-137 source. The samples were then analyzed by dielectric analysis (DEA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and Vickers microhardness. The MWNT/PMMA composites were found to show increased radiation hardness with respect to the glass transition temperature and mechanical properties. The dielectric properties were changed more significantly for the composites than for the neat PMMA. In addition, initial aging studies were performed on the irradiated samples after 3 months via DMA. The results indicate that multi-walled nanotubes may enhance radiation hardness of mechanical properties in PMMA. (C) 2004 Elsevier Ltd. All rights reserved.