Phase morphology, rheological, and mechanical properties of ultrahigh molecular weight polyethylene (UHMWPE)/PP/organo-montmorillonite nanocomposites were investigated in this work. The results of TEM and XRD indicated that the organo-montmorillonite PMM prepared with the complex intercalator [2-methacryloyloxy-ethyldodecyldimethylammonium bromide /poly(ethylene glycol)] were exfoliated and dispersed into UHMWPE matrix, and the synergistic effect of the complex intercalator on the exfoliation and intercalation for montmorillonite occurred. Besides, the presence of PMM in UHMWPE matrix was found able to lead to a significant reduction of melt viscosity and enhancement in tensile strength and elongation at break of UHMWPE, except that izod-notched impact strength was without much obvious change. The dispersed PMM particles exhibited a comparatively large two-dimensional aspect ratio (L-clay/d(clay) = 35.5), which played an important role in determining the enhancement of mechanical properties of UHMWPE nanocomposites. (c) 2007 Wiley Periodicals, Inc.