A spectroscopic study of the amino functionalization of double-walled carbon nanotubes (DWCNT) is performed. Original experimental investigations by near edge X-ray absorption fine structure spectroscopy at the C and O K-edges allow one to follow the efficiency of the chemistry during the different steps of covalent functionalization. Combined with Raman spectroscopy, the characterization gives direct evidence of the grafting of amino-terminated molecules on the structural defects of the DWCNT external wall, whereas the internal wall does not undergo any change. Structural and mechanical investigations of the amino functionalized DWCNT/epoxy composites show coupling between epoxy molecules and the DWCNTs. Functionalization improves the interface between amino-functionalized DWCNT and the epoxy molecules. Electrical transport measurements indicate a percolating network formed only by the inner metallic tubes of the DWCNTs. The activation energy of the barrier between connected metallic tubes is determined to be around 20 meV. © 2012 Elsevier Ltd. All rights reserved.