The degradation mechanism of polypropylene (PP)-clay nanocomposites is investigated in the present study. The PP-clay nanocomposites are prepared through a solution process with 4 and 8 wt % incorporation of nanoclay in a polymer matrix. Nanoclay with two types of organic modifications (25-30 wt % methyl dihydroxyethyl hydrogenated tallow ammonium (TA) and 25-30 wt 96 octadecylamine (OA)) is used with isotactic PP, atactic PP, and ethylene propylene copolymer with similar to 20 wt % rubber. Characterization of nanocomposites is done through X-ray diffraction (XRD) analysis while melting and crystallization behavior is studied through differential scanning calorimetry (DSC). XRD and DSC analysis shows formation of intercalated type nanocomposites with improved barrier properties. Degradation behavior of nanocomposites is studied through thermogravimetric analysis (TGA). Weight loss curves are further analyzed through the Friedman technique to find the rate of degradation. Nanoclay incorporation increases the lifetime of nanocomposites, calculated using an equation derived by Toop [IEEE Trans. Electr. Insul. 1971, 6, 2-14]. The peak rate of degradation in nanocomposites with isotactic homo PP and ethylene propylene copolymer is found to increase up to 1.5 times. Atactic homo PP and its nanocomposites show only a marginal improvement in properties as well as degradation rate. It is also concluded that the rate of degradation increased with clay loading due to increase in residual impurity.