Carbon nanotubes (CNTs) possess extremely high stiffness, strength, and resilience, and may provide ultimate reinforcing materials for the development of nanocomposites. In this paper, the effective material properties of CNT-based composites are evaluated based on the continuum mechanics using a hexagonal representative volume element (RVE). Numerical equations are used to extract the effective material properties from numerical solutions for the hexagonal RVEs under axial loading case. An extended rule of mixtures for estimating effective Young’s modulus in the axial direction of the RVE is applied. It has been observed that the addition of the CNTs in a matrix at volume fractions of only about 3.6%, the stiffness of the composite is increased by 33% for long CNT at , whereas not much improvement in stiffness has been noticed in the case of short CNTS at . Effectiveness of composites is evaluated in terms of various dimensions such as thickness, diameter, and length of CNT. These results suggest that short CNTs in a matrix may not be as effective as long CNTs in reinforcing a composite. The simulation results are consistent with the experimental ones reported in literature. Also, the comparative evaluation of all three types of RVEs is presented here.