Intermittent compression stress relaxation (CSR) testing was used to examine the degradation of a large scale chloroprene rubber (CR) O-ring, rather than a reduced scale copy, as well as predict its life-time. An intermittent CSR jig was designed by considering the O-ring’s environment during use. The testing allowed the observation of the effects of friction, heat loss and stress relaxation by the Mullins effect. Degradation of O-rings by thermal aging was observed between 40 and 120 ℃. In the high temperature range of 80-120 ℃, the O-rings exhibited linear degradation behavior and satisfied the Arrhenius relationship. The activation energy was approximately 72.7 kJ/mol. From the Arrhenius plots, the predicted life-times were 22.8 years and 34.5 years for the 50% and 40% failure conditions, respectively. Using the time-temperature superposition (TTS) principle, full predictions of failure at 40 ℃ could be made, saving considerable testing time. Between 40 and 80 ℃, the activation energy decreased to 58.9 kJ/mol. William-Landel-Ferry (WLF) plotting confirmed that the O-rings show non-linear degradation behavior under 80 ℃. The life-time of the O-rings predicted by the TTS principle was 11.1 years and 18.1 years for each failure condition. The life-time predicted by the TTS principle was more conservative than that from the Arrhenius relationship.