Two type of nanocomposites-an immiscible blend, high density polyethylene/polyamide 6 (HDPE/PA-6) with organomodified clay, and a compatibilized blend, high density polyethylene grafted with acrylic acid/PA-6 (PEAA/PA-6) with organomodified clay-were prepared via melt compounding. X-ray diffraction and transmission electron microscopy results revealed that the clay was intercalated and partially exfoliated. Positron annihilation lifetime spectroscopy has been utilized to investigate the free-volume hole properties of two type of nanocomposites. The results show a negative deviation of free-volume size in PEAA/PA-6 blend, and a positive deviation in HDPE/PA-6 blend, and 13 has a greater negative deviation in compatibilized blend than in immiscible blend due to interaction between dissimilar chains. For nanocomposites based on polymer blends, in immiscible HDPE/PA-6/organomodified clay system, the variation of free-volume size with clay content is not obvious and the free-volume concentration and fraction decreased. While in the case of compatibilized PEAA/PA-6/organomodified clay nanocomposites, complicated variation of free-volume properties due to interactions between two phases and organomodified clay was observed. And the interaction parameter P shows the interactions between polymers and organomodified clay. (c) 2006 Wiley Periodicals, Inc.