The current study focuses on improving the polyester's ability to protect against gamma radiation by utilizing a nanofiller made of Ni0.5Zn0.5Fe2O4. Therefore, four polyester samples doped by Ni0.5Zn0.5Fe2O4 nanoparticles with various concentrations were fabricated via the sol-gel auto-combustion technique. The characterization of the fabricated composites was performed experimentally using the XRD (Bruker AXS D8 Advanced diffractometer), EDX, and Fourier transform infrared spectroscopy. Besides, the scanning electron microscope and transmission electron microscope were applied in order to describe the particle size of the nano filers and the particle distribution of the additive nanofiller in the fabricated composites. Furthermore, the evaluation of the composites' γ-ray shielding characteristics was done using the Monte Carlo simulation method. According to the study, the inclusion of the nanofiller improved the linear attenuation coefficient of the existing polyester. For example, the linear attenuation coefficient at 662 keV was enhanced with a factor of ≈64% by raising the nanofiller concentration between 0 wt% and 40 wt%. The linear attenuation coefficient shows also a high decrease with a factor of ≈99%, when the photon energy raised from keV to 1332 keV, respectively, for the polyester sample reinforced by 40 wt% of the nanofillers.