The fast neutron and gamma-ray attenuation properties of pure high-density polyethylene and its composites were investigated, including 90 HDPE/10 B4C (wt%) and 60 HDPE/10 B4C/30X (wt%) (Where X represents iron oxide, aluminum oxide, iron, and aluminum). The examined samples were analyzed using ascanning electron microscope, and their mechanical properties were assessed. The composite of 60 HDPE/10 B4C/30 α-Fe2O3 (wt%) shows better mechanical properties than those of other composites under investigation. 239Pu–Be was used as asource of fast neutrons with a neutron yield of 1.7 × 106 n s−1 and was detected by the Stilbene scintillator. Neutron removal cross-section with dependent parameters, the mean free path and half-value layer of the prepared composites, were calculated. Furthermore, the gamma-ray transmission through the produced composites has been examined. The composite containing 30% iron oxide exhibited superior shielding characteristics for neutrons and gamma rays compared to the other analyzed samples. The computed values of the shielding characteristics indicate that the produced composites are highly effective for shielding fast neutrons and gamma rays in radiation facilities.