The effect of percolation threshold on the mechanical properties of insulate polymer nanocomposites has been briefly investigated in literature. In this work, an approach is suggested to study the percolation threshold and interphase role in polymer/clay nanocomposites (PCN) by a model for tensile modulus. The percolation threshold is related to the aspect ratio of clay layers and the predictions of the suggested methodology are compared with the experimental data. A low percolation threshold is obtained by high aspect ratio of clay layers which increases the modulus. Also, the developed model suggests the accurate results compared to experimental data assuming the interphase role. According to the calculations, the best modulus of PCN is achieved by the thinnest clay layers and the thickest interphase between polymer and clay. (C) 2016 Published by Elsevier Inc.