Short length vapor-grown carbon nanofibers (VGCNFs) were functionalized with 4-aminobenzoic acid in polyphosphoric acid/phosphorous phentoxide medium via "direct" Friedel-Crafts acylation reaction to afford aminobenzoyl-functionalized VGCNFs (AF-VGCNFs). The AF-VGCNFs as a cocuring agent were mixed with epoxy resin by simple mechanical stirring in methanol which was added to help efficient mixing. After evaporation of methanol, 4,4'-methylenedianiline as a curing agent was added to the mixture, which was then cured at elevated temperatures. The resultant composites displayed uniform dispersion of AF-VGCNFs into cured epoxy matrix. During curing process, the amine functionalities on AF-VGCNF together with 4,4'-methylenedianiline were expected to be involved in covalent attachment to the epoxy resin. As a result, both tensile modulus and strength of the composites were improved when compared with those of pure epoxy resin. Thus, the AF-VGCNFs play a role as an outstanding functional additive, which could resolve both dispersion and interfacial adhesion issues at the same time by functionalization of VGCNFs and covalent bonding between the additive and matrix, respectively. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7473-7482, 2008