The main goal of this study is to explicate the exact role of nanoclay particles on thermal degradation mechanism and crystallization behavior of blend-based nanocomposites. Thermoplastic olefin (TPO) nanocomposites, as a simple model, were prepared via melt mixing in an internal batch mixer. X-ray diffractometry (XRD) and transmission electron microscopy tests show that a relatively good dispersion of silicate layers was obtained in the system. On the addition of nanoclay, a remarkable reduction in rubber domain size was observed through scanning electron microscopy (SEM). Thermogravimetric analysis shows that nanoclay particles can retard thermal decomposition process. Thermal degradation kinetic studies, using Flynn-Wall-Ozawa method, reveal that addition of nanoclay contents higher than 1 wt % changes the mechanism of thermal degradation. A mechanism was proposed to explain this phenomenon based on SEM images of char residues. Non-isothermal crystallization behavior of samples was investigated using differential scanning calorimeter. The unexpected reduction in crystallinity of TPO nanocomposites containing 5 wt % nanoclay was explained using rheometry analysis and attributed to the formation of stable percolated clay networks in this sample. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2492-2499, 2012