Pyridinium- and phosphonium-based filler surface modifications (tetraphenylphosphonium, hexadecylpyridinium and hexadecyltriphenylphosphonium), which are more thermally stable than the conventionally used ammonium modifications, were exchanged on the filler surface. Polypropylene nanocomposites with the modified fillers were prepared and characterized for gas barrier, mechanical, calorimetric and thermal properties. Mixed morphology consisting of single layers and tactoids of different thicknesses was observed in the composites. The developed morphology in the composites was a result of better thermal stability of the system as well as the nature of the surface modification. Though the completely aromatic surface modification was most thermally stable, it did not improve the composite properties significantly owing to poor interfacial intermixing with the polymer. On the other hand, impressive improvements in the gas barrier and mechanical properties were observed for the filler modifications which included long alkyl chains. These improvements were also better than the corresponding ammonium modifications. The incorporation of the filler led to enhanced thermal resistance of the composites.