In the present study, the role of micro-size pozzolana in the enhancement of the radiation shielding properties of high-density polyethylene (HDPE) was investigated. Therefore, HDPE polymers reinforced by various ratios of pozzolana were fabricated. The density of the fabricated composites increased from 0.089 g/cm3 to 1.234 g/cm3, as measured using the MH-300A density meter. Additionally, the linear attenuation coefficient for the fabricated composites was measured at energies of 59 keV, 662 keV, and 1252 keV emitted by the isotopes Am-241, Cs-137, and Co-60, respectively. The experimental measurements show an increase in the linear attenuation coefficient from 0.12 cm−1 to 0.82 cm−1 at γ-ray energy of 59 keV. The enhancement in the linear attenuation coefficient affects the half-value thickness and transmission factor where the half-value thickness decreased from 5.73 cm to 0.84 cm and the transmission factor decreased from 88.60% to 43.87%, raising the pozzolana concentration between 0 wt% and 50 wt%.