The thermal behaviour of ultra-high molecular weight polyethylene (UHMWPE) of different molecular weights was examined by thermal analysis methods. The melting temperatureTm and the heat of melting δH were measured by the DSC method. The thermooxidative degradation process was investigated by using a MOM Q-1500 D derivatograph at various heating rates in air atmosphere. The initial decomposition temperatureTi was determined from the TG curves, and other characteristic temperatures of decomposition were calculated. It was found thatTm and δH are higher for UHMWPE than those for HDPE, i.e. 146‡C and 195 J g−1 for UHMWPE as compared with 133‡C and 166 J g−1 for HDPE. The thermal behaviour of the investigated UHMWPE samples is not significantly influenced by molecular weight.