Abstract The photo-decomposition of secondary hydroperoxide groups accumulated in γ-oxidized linear low density polyethylene films was examined. Through natural and accelerated UV exposure, either in vacuo or in the presence of air, we found that hydroperoxides were the precursors for the formation of vinyls and secondary alcohols. In contrast, it is still unclear whether acid groups come from hydroperoxides. The comparison of results obtained under vacuum and in the presence of air shed some light on the formation of esters and ketones. Classical FTIR as well as derivatization techniques (NO and SF 4 treatments) were used to monitor the hydroperoxide photo-decomposition and quantify the oxidation outcomes.