Together with residual host neurons, transplanted neural stem cell (NSC)-derived neurons play a critical role in reconstructing disrupted neural circuits after spinal cord injury (SCI). Since a large number of tracts are disrupted and the majority of host neurons die around the lesion site as the damage spreads, minimizing this spreading and preserving the lesion site are important for attaining further improvements in reconstruction. High mobility group box-1 (HMGB1) is a damage-associated molecular pattern protein that triggers sterile inflammation after tissue injury. In the ischemic and injured brain, neutralization of HMGB1 with a specific antibody reportedly stabilizes the blood-brain barrier, suppresses inflammatory cytokine expression, and improves functional recovery. Using a SCI model mouse, we here developed a combinatorial treatment for SCI: administering anti-HMGB1 antibody prior to transplantation of NSCs derived from human induced pluripotent stem cells (hiPSC-NSCs) yielded a dramatic improvement in locomotion recovery after SCI. Even anti-HMGB1 antibody treatment alone alleviated blood-spinal cord barrier disruption and edema formation, and increased the number of neurites from spared axons and the survival of host neurons, resulting in functional recovery. However, this recovery was greatly enhanced by the subsequent hiPSC-NSC transplantation, reaching an extent that has never before been reported. We also found that this improved recovery was directly associated with connections established between surviving host neurons and transplant-derived neurons. Taken together, our results highlight combinatorial treatment with anti-HMGB1 antibody and hiPSC-NSC transplantation as a promising novel therapy for SCI. Stem Cells 2018;36:737-750.