Nanocomposites hierarchical structure, ranging from nano to macro length-scales, urges to account for the characteristic phenomena of the different involved length-scales and to bridge their effects up to the macroscale. This makes the assessment of nanocomposite mechanical properties a challenging task. In the present work, a model to assess the nanocomposite toughening due to plastic yielding of nanovoids is presented. The model accounts for the emergence of an interphase, created by the inter-and supra-molecular interactions arising at the nanoscale, with mechanical properties different from those of the matrix. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICM11