Carbon nanotubes were grown directly on carbon fibers using chemical vapor deposition. When embedded in a polymer matrix, the change in length scale of carbon nanotubes relative to carbon fibers results in a multiscale composite, where individual carbon fibers are surrounded by a sheath of nanocomposite reinforcement. Single-fiber composites were fabricated to examine the influence of local nanotube reinforcement on load transfer at the fiber/matrix interface. Results of the single-fiber composite tests indicate that the nanocomposite reinforcement improves interfacial load transfer. Selective reinforcement by nanotubes at the fiber/matrix interface likely results in local stiffening of the polymer matrix near the fiber/matrix interface, thus, improving load transfer.