This research aimed to study the effect of different procedures for carbon nanotube (CNT) dispersion and functionalization in an epoxy matrix, following their effects on the mechanical and dynamic mechanical properties. In first instance, ionic liquid (IL) 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMImNTf2) was identified as the best dispersant for unmodified CNT dispersion, compared to acetone and sodium dodecyl sulfate (SDS). Further optimization of the nanocomposite formulation was pursued through the dispersion of ten different chemically treated types of functionalized-CNT, plus an alternative route was performed by using the IL 1-n-butyl-3-methylimidazolium chloride-BMImCl. The aim was to improve the nanofiller’s functionalization, since this is directly related to the interaction and dispersion of nanoparticles into the polymer matrix. The association of IL BMImNTf2 dispersant with oxidized CNT provided high-performance epoxy/CNT nanocomposites, when the oxidation was promoted by a unique treatment, especially sulfuric acid or plasma application. It was sought to maximize most of the nanocomposites properties produced by combining the effect of oxidation with the application of ionic liquids, which are substances with high stabilization character. Compared to the neat resin, the nanocomposite treated via acid > O2 plasma > amination was 60% harder, and its T g increased from 104 °C to 110 °C. In contrast, treatments with surfactant and acetone weakened the CNT, resulting in a T g between 96 and 98 °C for nanocomposites.