Traumatic spinal cord injury (SCI) induces tissue damage and results in the formation of a cavity that inhibits axonal regrowth. Filling this cavity with a growth-permissive substrate would likely promote regeneration and repair. Single-walled carbon nanotubes functionalized with polyethylene glycol (SWNT-PEG) have been shown to increase the length of selected neurites in vitro. We hypothesized that administration of SWNT-PEG after experimental SCI will promote regeneration of axons into the lesion cavity and functional recovery of the hindlimbs. To evaluate this hypothesis, complete transection SCI was induced at the T9 vertebral level in adult female rats. One week after transection, the epicenter of the lesion was injected with 25 μL of either vehicle (saline), or 1 μg/mL, 10 μg/mL, or 100 μg/mL of SWNT-PEG. Behavioral analysis was conducted before injury, before treatment, and once every 7 days for 28 days after treatment. At 28 days post-injection the rats were euthanized and spinal cord tissue was extracted. Immunohistochemistry was used to detect the area of the cyst, the extent of the glial scar, and axonal morphology. We found that post-SCI administration of SWNT-PEG decreased lesion volume, increased neurofilament-positive fibers and corticospinal tract fibers in the lesion, and did not increase reactive gliosis. Additionally, post-SCI administration of SWNT-PEG induced a modest improvement in hindlimb locomotor recovery without inducing hyperalgesia. These data suggest that SWNT-PEG may be an effective material to promote axonal repair and regeneration after SCI. © Copyright 2011, Mary Ann Liebert, Inc.