Polypropylene (PP) nanocomposites were prepared using montmorillonite with different organic modifiers, and the effect of processing aid (EMCA and PPG) on the dispersion of the nanofillers in the PP matrix was evaluated by WAXD, TEM, DSC, TGA, DMA, and mechanical tests. The present study helps to clarify the effects of the organic modifiers of clays on the intercalation and exfoliation processes. Nanocomposites of intercalated and partially exfoliated morphology were obtained, mainly when a low amount (1:1) of PP-g-MA/MMT was used. The results of the tests on mechanical properties showed that the clays with larger d(001), (C-15A and Nanofil 5) using PPG presented a more considerable gain in impact strength. The nanocomposites using clays with smaller d(001)(C-20A) presented larger modulus when compared with those of pristine PR The heat deflection temperature, crystallization temperature, and thermal stability of the nanocomposites were improved compared to neat PR The DMA results showed that the organoclay improved the modulus of PP, but decreased the T-g. (C) 2008 Wiley Periodicals, Inc. J Polyin Sci Part B: Polym Phys 46: 2519-2531, 2008