The advancement in nuclear science and technology have fostered the use of ionizing radiations in diverse sectors including medical radiation facilities, nuclear research laboratories, industrial gauging, food irradiation, geological exploration, military and security operations. making radiation exposure indispensable for the mankind. Considering the adverse effect of prolonged radiation exposure on human health, radiation shielding and protection are the issues of paramount importance. In view of this, epoxy-based nanocomposites are emerging to be a state-of-the-art X-ray and g-ray shielding alternatives to conventional materials such as lead, metals, glass composites, ceramics and concretes. In this study, bismuth (III) oxide (Bi2O3) decorated graphene oxide (GO) nanocomposites were employed as novel radioprotective fillers in the epoxy polymer matrix. Simple solution casting technique was used to synthesize the epoxy nanocomposites containing surface decorated Bi2O3 fillers. The thermo-mechanical and radiation shielding properties of the composites were studied as function of filler loading (0, 5, 10 and 15 wt%). These nanocomposites displayed good thermal resistance (~ 450 °C), high elastic modulus (~ 4.36 GPa) and storage modulus, thereby confirming the improved dispersion and better interfacial adhesion in the composites. The formation of continuous filler network across epoxy matrix significantly improved the X-ray and g-ray shielding properties of these composites in the wide energy range of medical interest (30 – 1332 keV). Appreciable enhancement in radiation attenuation characteristics of the newly developed material is mainly due to the synergistic shielding effect of combining high-Z metal oxide fillers and GO. Shielding efficiency of these lowly loaded epoxy/BGO composites were comparable with the composites containing Bi2O3 nanoparticles alone and highly loaded microcomposites.