Functionalized multiwalled carbon nanotubes (f-MWCNTs) have been introduced into immiscible polypropylene/ethylene-co-vinyl acetate (PP/EVA) blends. Two different compositions, one (PP/EVA=80/20) exhibits the typical sea-island morphology and the other (PP/EVA=60/40) exhibits the cocontinuous morphology, have been prepared with different contents of f-MWCNTs. The impact measurement shows that f-MWCNTs induce the great improvement of fracture toughness of cocontinuous PP/EVA blends. The results based on the morphologies and the rheological properties of the composites suggest that, a local "single-network structure" of f-MWCNTs exists in PP/EVA (80/20) system whereas a "dual-network structure" of f-MWCNTs and EVA phase exists in PP/EVA (60/40) system, and the latter structure accounts for the largely improved fracture toughness of the composites. (C) 2009 Elsevier Ltd. All rights reserved.