Depending on the level of applied potential for a given DC electric field, the alignment behavior could be controlled [24], namely deposition of SWCNTs on the electrode surface as a nanostructured carbon film at a low potential (∼40 V) and linear bundles extending across the space between the two electrodes at a high field (>100 V). It was also demonstrated that both dispersion and alignment of oxidized MWCNTs were better than pristine MWCNTs under an AC electric field [26]. Experiments aimed at aligning CNTs using electric fields have mostly been carried out in dilute solutions during solvent evaporation or filtration. Few experiments have been reported of CNT alignment in polymers mainly using small specimens of several millimeters. Zhu et al. [27] demonstrated AC electric field-induced alignment of MWCNTs in epoxy bulk nanocomposites prepared by a layer-by-layer method, where both the storage modulus and electrical conductivity were significantly enhanced in the alignment direction. However, amine functionalized CNTs showed lower electrical conductivities than the pristine CNTs after alignment. A method was also devised to align CNTs using a flow field where the surfactant solution containing SWCNTs was slowly injected through a syringe needle into a PVA solution [28], where the alignment was maintained due to the shear contribution in the flow at the tip of the needle. Electrospinning is another technique that can be used to in situ align CNTs in polymer nanofibers [29] and [30]. The present study is aimed at evaluating the alignment behaviors of MWCNTs at varying concentrations in different media by DC electric fields of different potentials. The alignment behaviors are correlated with the electrical, mechanical and fracture properties of the nanocomposites. Special emphasis is placed on understanding the anisotropic electrical conductivities and fracture toughness measured of the composites with aligned CNTs of different contents.