The effect of covalent functionalization of (5,5)/(10,10)/(15,15) three-wall carbon nanotubes (3WCNTs) on the atomic-level mechanical properties of 3WCNT-reinforced vinyl ester epoxy polymer has been studied using molecular mechanics calculations. Inter- and intra-molecular atomic interactions in the 3WCNT + vinyl ester epoxy polymer system are represented using condensed-phased optimized molecular potential for atomistic simulation studies (COMPASS), an ab initio forcefield that enables an accurate and simultaneous prediction of various gas-phase and condensed-phase properties of organic and inorganic materials. The computational crystal consisting of a periodic array of infinitely long 3WCNTs surrounded by amorphous poly-vinyl-ester-epoxy is constructed using an in-house developed computer program and the amorphous cell tools by Accelrys. All the computations are carried out using Discover, a molecular statics/dynamics program from Accelrys. The results obtained show that covalent functionalization has a profound effect of the matrix-to-nanotube load transfer especially when the loads are applied in a direction orthogonal to the nanotube axis. (c) 2006 Elsevier B.V. All rights reserved.