The thermal behaviour of low-density polyethylene (LDPE) as powder and pellet have been characterised by means of the emanation thermal analysis (ETA) during heating in air. The ETA was used in the study of LDPE polymer before and after irradiation to various doses of high energy electrons. It was shown that the ETA reflects microstructure changes taking place as the result of thermal degradation and oxidation pyrolysis of the polymer samples. It was shown in the study of LDPE products, resulting after the electron-beam treatment, that the results of ETA reflect structural changes caused by the radiation over the range of absorbed doses from 0 to 20 MGy. The annealing chemical radicals produced by the electron-beam irradiation was assessed by comparing ETA curves measured during first and second heating runs.