Amino-functionalization of multiwalled carbon nanotubes (MWCNTs) was carried out by grafting triethylenetetramine (TETA) on the surfaces of MWCNTs through the acid-thionyl chloride way. The amino-functionalized MWCNTs show improved compatibility with epoxy resin and, as a result, more homogenous dispersion in the matrix. The mechanical, optical, and thermal properties of the amino-functionalized MWCNT/epoxy composites were also investigated. It was found that introducing the amino-functionalized MWCNTs into epoxy resin greatly increased the charpy impact strength, glass transition temperature, and initial decomposing temperature of cured epoxy resin. In addition, introducing unfunctionalized MWCNTs into epoxy resin was found greatly depressing the light transmission properties, which would affirmatively confine the application of the MWCNTs/epoxy composites in the future, while much higher light transmittance than that of unfunctionalized MWCNTs/epoxy composites was found for amino-functionalized MWCNTs/epoxy composites. SEM of the impact cross section and TEM of ultrathin film of the amino-functionalized MWCNTs/epoxy composites showed that the amino-functionalized MWCNTs were wetted well by epoxy matrix. (c) 2006 Wiley Periodicals, Inc.