Double-walled carbon nanotubes (DWCNTs) and multiwalled carbon nanotubes (MWCNTs) were modified using melamine to attach -NH2 to the surface of these fillers, without previous oxidation of their graphene layers. FT-Raman, elemental (chemical) and thermogravimetric analysis, confirmed the modification, which was more extensive for DWCNTs. The potential of this modification was evaluated by adding the melamin-modified nanotubes to thermosets based on diglycidyl ether of bisphenol A (resin) and polycyclic amine (hardener). Broadening of the glass transition interval and an increase between 7 and 8 degrees C of the glass transition temperatures show better filler/matrix interaction for the nanocomposites based on melamine-modified nanotubes. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1860-1868, 2009