Using Monte-Carlo techniques, we study polymer chain conformations near nanoparticles for dense melts of high molecular weight. Our results indicate the presence of a thin interfacial region (1-2 nm in thickness) within which polymer segments orient tangentially to the particle surface causing a stretching and widening of the chain ellipsoid. That region is also characterized by an accumulation of chain ends and a decrease in polymer density. Nanoparticles also affect polymer properties far away into the bulk. Thus, at small particle radius, we observe an overall swelling of the polymer chains when the distance between the centers of mass of nearest-neighbor particles becomes smaller than the radius of gyration of the chains. (C) 2008 Elsevier Ltd. All rights reserved.