Nanoclay composites based on polypropylene (PP)/polystyrene (PS) blends were prepared by melt mixing in a Thermo Haake Rheochord mixer. The effect of modified clays on the properties of nanocomposites has been studied. The degree of dispersion and morphology of nanocomposites were evaluated from X-ray diffraction and Scanning electron microscopy. Nanocomposites prepared from modified clays show improved tensile modulus and strength as compared to those prepared from unmodified clay. Vinyl silane modified nanocomposites show maximum improvement in mechanical properties, suggesting that vinyl silane provides better interfacial interaction. Thermogravimetric analysis shows improved thermal stability of PP/PS/clay nanocomposites. The dynamic mechanical analysis reveals higher storage moduli over a temperature range of 40-125 degrees C for nanocomposites, and the extent of increase in the storage modulus is dependent on the type of clay. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013