This study investigated the effects of Pb₂O₃ nanoparticles on the thermal, mechanical, and shielding properties of epoxy resin, liquid silicone rubber, and polyvinyl chloride composites which have been proposed as efficient substitutes for traditional lead-based materials for shielding gamma and X-ray radiations. The Pb₂O₃ nanoparticles were synthesized using a low-cost electrochemical method, characterized by XRD and SEM analysis, and uniformly dispersed in the polymer matrix by casting technique. The mechanical and thermal properties of the samples were investigated by stress-strain and TGA analysis, and the effectiveness of Pb₂O₃ in improving the radiation shielding capabilities of the polymers was investigated by analyzing parameters such as the mass attenuation coefficients and the half-value layer factor for gamma rays. The results showed that the addition of Pb₂O₃ nanoparticles had no adverse effect on the thermal stability of polyvinyl chloride (PVC) composites; at the same time, it decreased the thermal stability and increased the weight loss of Epoxy Resin (ER) and Liquid Silicon Rubber (LSR) composites. The nanocomposites had higher tensile strength and modulus of elasticity than the original polymer, and their shielding properties improved with increasing nanofiller content. This study provides insights into modifying the properties of composites using fillers and polymers to improve their properties for various applications.