This paper explores the effect of nanoclay orientation on the long term thermal stability of a polyethylene (PE)/nanoclay nanocomposite. Nanoclay morphology and orientation in an injection molded PE-clay nanocomposite bar were examined using transmission electron microscopy and simultaneous small angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD). These nanocomposites were aged at elevated temperatures for various periods of time, and the relative amount of antioxidant (AO) was monitored using an oxidative induction time test. The presence of 4 wt% nanoclay accelerates AO depletion, particularly at the surface region of the sample. AO concentration profiles along different directions of the sample bar were constructed based on SAXS/WAXD results, and were correlated with the clay orientation. A detailed AO depletion mechanism is discussed. (C) 2013 Elsevier Ltd. All rights reserved.