Directly functionalized multiwalled carbon nanotubes (MWCNTs) with benzene-1,3,5-tricarboxylic acid (BTC) and 3,5-diaminobenzoic acid (DAB) were successfully accomplished with less structural damage as confirmed by XPS and FT-Raman results. Their dispersibility and thermal stability were achieved after the functionalization. The functional groups on MWCNT surfaces can accelerate the curing reaction of epoxy composites remarkable inducing rather low exothermic peak temperature (Tp) and exothermic heat of reaction (ΔH). The values of activation energy (Ea) obtained from Kissinger and Ozawa methods obviously decreased with the introduction of MWCNTs, especially DAB-MWCNTs. The dynamic mechanical properties notably enhanced with the incorporation of unmodified and functionalized MWCNTs. The crosslink density (ρ) increased and free volume fraction (fg) decreased, resulting in dramatic increase of glass transition temperatures (Tg) and decrease of coefficient of thermal expansion. Additionally, epoxy composites exhibited low dielectric constant close to that of neat epoxy resin. From these remarkable properties, MWCNT/epoxy composites can be considered as a good candidate for high performance insulation materials. POLYM. ENG. SCI., 53:2194–2204, 2013. © 2013 Society of Plastics Engineers