The linear and nonlinear shear rheological behaviors of poly(propylene) (PP)/clay (organophilic-montmorillonite) nanocomposites (PP/org-MMT) were investigated by an ARES rheometer. The materials were prepared by melt intercalation with maleic anhydride functionalized PP as a compatibilizer. The storage moduli (G'), loss moduli (G"), and dynamic viscosities of polymer/clay nanocomposites (PPCNs) increase monotonically with org-MMT content. The presence of org-MMT leads to pseudo-solid-like behaviors and slower relaxation behaviors of PPCN melts. For all samples, the dependence of G' and G" on omega shows non-terminal behaviors. At lower frequency, the steady shear viscosities of PPCNs increase with org-MMT content. However, the PPCN melts show a greater shear thinning tendency than pure PP melt because of the preferential orientation of the MMT layers. Therefore, PPCNs have higher moduli but better processibility compared with pure PP. (C) 2003 Wiley Periodicals, Inc.