The present research prepared samples of pure high-density polyethylene (HDPE)/boron carbide reinforced with iron dioxide, aluminum dioxide, iron, and aluminum. The effectiveness of the prepared samples as a shielding material against gamma-rays and their thermal and dielectric properties have been evaluated. The shielding characteristics of the prepared composites were investigated theoretically using the Phy-X/PSD program and experimentally for gamma-rays emitted from 131Cs and 60Co radioactive isotopes. The shielding evaluation included the mass attenuation coefficient (μ /ρ), half value layer (HVL), mean free path (MFP), atomic and electronic cross-sections (σa & σe), effective atomic number and electron density (Zeff &Neff), and exposure buildup factor (EBF). The EBF peaks of samples containing Fe and Fe2O3 are 103 times lower than pure HDPE. The results indicate that samples C2 and C3 have a higher ability to protect against gamma radiation than that of the other investigated samples. X-ray diffractometer (XRD) spectrum shows that adding B4C, Fe, Fe2O3, Al, and Al2O3 to HDPE caused an increase in its full width at half maximum (FWHM) value and a decrease in its average crystallite diameters (D) at its primary characteristic scattering angle of 21.49◦. Adding multiple types of fillers to HDPE results in a minor shift in the melting temperature of the hosting matrix as proved from differential scanning calorimetry (DSC) data. The composite of HDPE/B4C/Al2O3 60/10/30 demonstrated the most significant values of dielectric parameters in comparison with the other composites, in good accord with the XRD results. The ac conductivity relied on the dopant type in the hosting matrix; the highest value was observed for HDPE/B4C/Al2O3 composite.