Abstarct: With the increasing applications of X-rays and gamma rays in various fields such as medicine, industry, and agriculture, the need for protection against these radiations has become more pressing. Traditional materials like lead, due to their high density and atomic number, have a good ability to attenuate these radiations; however, their environmental problems and high weight have necessitated the search for suitable alternatives. In this research, focusing on novel materials, the potential of polymeric nanocomposites in shielding against ionizing radiation is investigated. Initially, the various interactions of radiation with matter and the importance of parameters such as atomic number and density in radiation attenuation are examined. Subsequently, considering the unique properties of nanoparticles like high surface area and uniform dispersion, their application in improving the shielding properties of composites is studied. Continuing the research, polymeric composites reinforced with nano and micro-sized magnesium oxide (MgO) particles (with dimensions of 1 μm and 100 nm, respectively, at weight percentages of 25-50%) and cerium oxide (CeO2) nanoparticles (with dimensions of 100 nm at weight percentages of 30-70%) were investigated as potential candidates for protective coatings. Using the MCNPX simulation code, the shielding properties of these composites were modeled and compared to traditional materials. The simulation results indicated that the proposed composites, in addition to being lighter, more flexible, and more environmentally friendly than lead, exhibited a satisfactory ability to attenuate X-rays and gamma rays. In this regard, the MCNPX Monte Carlo simulation code was initially employed to design and simulate the desired structure. To evaluate its performance in attenuating X-ray and gamma radiation, crucial parameters such as mass attenuation coefficient (LAC), mass attenuation coefficient (MAC), buildup factor (BF), mean free path (MFP), shielding effectiveness (SR%), transmission factor (TF), lead equivalent thickness (LEV), and relative mass changes were calculated. Additionally, the calculations were validated against experimental XCOM data and established standards. Subsequently, to investigate the impact of particle size, by calculating the relative difference in shielding parameters for nano and microparticles, it was determined that nanoparticles, due to their more uniform distribution, yielded better performance. In the next phase, the shielding parameters were analyzed to identify the optimal filler weight percentage to evaluate the lead equivalent thickness for the optimal sample. baxsed on the investigations, it was found that the PVC polymer composite with 50% weight percent of magnesium oxide nanoparticles, as the optimal weight percentage, resulted in a reduction in the weight of the gamma radiation protective coating at energies of 0.662 MeV and above. This weight reduction was equivalent to 31.95%, 43.29%, and 26.53% of the lead protective coating at energies of 0.662, 1.173, and 1.332 MeV, respectively. Similarly, this weight reduction for the PVC polymer composite was equivalent to 36.46% and 13.11% less weight compared to lead coatings in the energy range of 1.173 and 1.332 MeV. Finally, to conduct experimental investigations, a prototype was fabricated using the solution casting method of these composites for application in X-ray and gamma radiation protective coatings. The fabricated samples included pure polymer film, PVC polymer microcomposite film with 25-50% weight percentage micro MgO filler, and PVC polymer nanocomposite film with 30-70% weight percentage nano CeO2 filler. Initially, to examine the structure of the fabricated samples, FE-SEM morphology and microstructure analyses were performed. Additionally, to investigate the absence of impurities, X-ray spectra were examined using XRD analysis. Furthermore, for evaluating mechanical properties, the tensile test was done. Ultimately, by analyzing the sub-photopeak areas, the linear attenuation coefficient of the samples was evaluated.