The preparation of exfoliated polymer nanocomposites (PNC) in nonpolar system is still preoccupying researchers in the domain. The ball milling coupled with melt-compounding was used for the preparation of polypropylene/montmorillonite PNC to evaluate the potential of ball milling in the improvement of clay dispersion. Different approaches were used for doing a preliminary ball milling of clay with or without coupling agent and of all components prior to melt-compounding. The microstructure as well as the rheological and the dynamic mechanical behaviors of the PNC compounds were characterized. The best improvements in clay dispersion were obtained by ball milling clay in the presence of other components to reduce particle agglomeration. The rheological behavior of the compounds confirmed their microstructure. The thermomechanical properties of PNC showed an enhancement in the storage modulus in the glassy and the rubbery states, independent of their microstructure. POLYM. ENG. SCI.,, 49:651-665, 2009. (c) 2009 Society of Plastics Engineers