The photodegradation behavior of ethyleneoctene copolymer (EOC) and EOC stabilized with UV stabilizers (Tinuvin 326, Chimassorb 81, Tinuvin 770 and Chimassorb 944) were investigated by the digital photography, color difference, gel content, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and mechanical tests. The results revealed that EOC exhibited a very poor photostability, whose performances were sharply reduced with increasing the irradiation time. The photodegradation products consisted of the carbonyl, hydroxyl and vinyl groups. The additives all showed an excellent photostabilizing effect, which effectively inhibited the gel formation and the chain photooxidation. The photostabilizing efficiency of these UV stabilizers could be ranked as Tinuvin 326 < Chimassorb 81 < Tinuvin 770 and Chimassorb 944. The secondary crystallization behavior was strongly affected by the annealing and chain scission. The chain scission, rather than the annealing, played a greater role in the secondary crystallization of the chain segments. And the serious chain scission could improve the mobility of the chain segments, which sharply promoted their crystallizability. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013