In this work, vapor-grown carbon nanofibers (CNFs) were functionalized using an optimized route and dispersed in the matrix of carbon fabric-reinforced epoxy composites to develop multiscale carbon/epoxy composites. Functionalization was carried out through an oxidative treatment with a mixture of HNO3/H2SO4 (1 : 3) using a combination of ultrasonication and magnetic stirring. Functionalized CNFs (F-CNFs) were characterized for their morphology, length, functional groups, and degradation due to oxidative treatment. The results showed that it was possible to efficiently functionalize CNFs without any degradation through proper selection of treatment duration. F-CNFs were dispersed homogeneously into the epoxy matrix using ultrasonication in combination with high-speed mechanical stirring. The incorporation of 0.1 wt % F-CNFs led to a 65% increase in Young's modulus and a 36% in tensile strength of neat carbon/epoxy composites. The fracture surfaces were studied using scanning electron microscopy to understand the property enhancement due to F-CNFs. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012