The effects of hindered amine light stabilizers (HALS) on the radiation—in,¬, duced discoloration of polyethylene (PE) are studied by measuring the yellowness index (YI) of PE. It is found that all the HALS used are effective in preventing PE from radiation — induced discoloration. The YI of PE added pentamethyl HALS (PMPM, PPMPM) is a little higher than that of PE added corresponding tetramethyl HALS (TMPM, PTMPM) when radiation dose is lower than 100kGy, but when the radiation dose is higher than 100kGy, the YI of PE added pen,¬, tamethyl HALS is lower. Pentamethyl HALS is more effective in preventing PE from radiation—induced discoloration when radiation dose is higher. It is also found that polymeric HALS is more effective in preventing PE from radiation — induced discoloration than corresponding monomeric HALS when radiation dose is higher than 200kGy. The formation of alkyl free radical,carbonyl after irradiation is measured. It is found that the relative concentration of free radical formed in PE added TMPM is higher than that of PE added PMPM when radiation dose is relatively high. The carbonyl index of PE containing pentamethyl HALS is less than that of PE containing tetramethyl HALS when radiation is relatively low, but the result is contrary when radiation dose is relatively high. It is believed that HALS prevents PE from radiation — induced discoloration by scavenging free radicals formed in irradiated PE.