We have studied an effect of three types of modifications of carbon nanotubes (CNTs) on dispersion and mechanical properties of final epoxy-amine based nanocomposites. First approach includes end-walled covalent chemical modification at the ends of nanotubes. The second one is side-walled covalent chemical modification along the whole length of nanotubes. The third procedure is noncovalent, physical modification done by the CNT surface coating with polyaniline. The modification of nanotubes was determined by X-ray photoelectron spectroscopy. The prepared epoxy-amine nanocomposites were characterized by dynamic-mechanical analysis, tensile testing, light microscopy, transmission electron microscopy, and thermogravimetry. We observed an improvement of the mechanical properties and the thermal stability by addition of the carbon nanotubes to the epoxy matrix. The strong interactions between the nanotube and the polymer matrix were discovered in the nanocomposites with physically modified nanotubes. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers