Recently, locomotor training has been shown to improve overground locomotion in patients with spinal cord injury (SCI). This has triggered renewed interest in the role of exercise in rehabilitation after SCI. However, there are no mouse models for voluntary exercise and recovery of function following SCI. Here, we report voluntary wheel running improves recovery from a SCI in mice. C57Bl/10 female mice received a 60-kdyne T9 contusion injury with an IH impactor after 3 weeks of voluntary wheel running or 3 weeks of standard single housing conditions. Following a 7-day recovery period, running mice were returned to their running wheels. Weekly open-field behavior measured locomotor recovery using the Basso, Beattie and Bresnahan (BBB) locomotor rating scale and the Basso Mouse Scale (BMS) locomotor rating scale, a scale recently developed specifically for mice. Initial experiments using standard rung wheels show that wheel running impaired recovery, but subsequent experiments using a modified flat-surface wheel show improved recovery with exercise. By 14 days post SCI, the modified flat-surface running group had significantly higher BBB and BMS scores than the sedentary group. A repeated measures ANOVA shows locomotor recovery of modified flat-surface running mice was significantly improved compared to sedentary animals (p < 0.05). Locomotor assessment using a ladder beam task also shows a significant improvement in the modified flat-surface runners (p < 0.05). Finally, fibronectin staining shows no significant difference in lesion size between the two groups. These data represent the first mouse model showing voluntary exercise improves recovery after SCI.