© Avestia Publishing, 2016.CNTs (carbon nanotubes) are ideal reinforcing materials for high strength polymer nanocomposites because of their high stiffness, strength and resilience properties. CNT-matrix interface is one of the parameters effecting the stiffness of nanocomposites. In this study, the effect of CNT-matrix interface properties on the effective global stiffness of nanocomposites is investigated numerically. A representative volume element (RVE) is modeled by using the finite element method (FEM) to predict the elastic behavior in micro level. The finite element model consists of three phases namely matrix, CNT and interphase. The stiffness is obtained from the elastic response of RVE subjected to an axial loading. The stiffness values are obtained for several thickness and modulus values of the interface and the waviness of CNT. Effective global stiffness is calculated by using Mori-Tanaka method where CNTs have varying amount of waviness, interphase properties and random orientations. It is found that there are significant effects of the interface on the effective global stiffness.