The nanocomposites of ethylene octene copolymer (Engage (R)) with an organically modified (dimethyldioctadecyl quaternary ammonium chloride) montmorillonite (M-MMT) clay were synthesized by using a solution intercalation technique. The intercalation of M-MMT layers for M-MMT loading of 2.5-7.5% was verified by the shift of X-ray diffraction peak to a lower angle, showing change in basal d-spacing from 1.26 for M-MMT to 1.35 nm. Internal structure and the dispersion state of M-MMT in the nanocomposites were observed by transmission electron microscope, which confirmed the clay in the intercalated state. Thermomechanical analysis results showed improved dimensional stability under compression at 30 degrees C for nanocomposites with increasing M-MMT. By DMA, the storage moduli of nanocomposites below glass transition temperature were higher than the neat Engage and increased with increasing M-MMT content. The glass transition temperature was lowest for the nanocomposite containing 2.5% M-MMT (E-2.5M-MMT), suggesting the optimal concentration of M-MMT in nanocomposite being 2.5% or higher from the viewpoint of thermal properties. The oxidation induction time (OIT) of the nanocomposites was obtained by using pressure-differential scanning calorimeter. The Engage/M-MMT nanocomposites were superior in thermal oxidation resistance as compared to the neat Engage, with E-5.0M-MMT yielding highest OITtime value.