Neuronal injuries have been a challenging problem for treatment, especially in the case of complete and chronic cervical spinal cord injury (SCI). Recently, particular attention is paid to the potential of stem cell in treating SCI, but there are only few clinical studies and insufficient data. This study explored the efficacy of autologous bone marrow mesenchymal stem cells (BMMSCs) transplantation in the treatment of SCI. Forty patients with complete and chronic cervical SCI were selected and randomly assigned to one of the two experimental groups, treatment group and control group. The treatment group received BMMSCs transplantation to the area surrounding injury, while the control group was not treated with any cell transplantation. Both the transplant recipients and the control group were followed up to 6 months, postoperatively. Preoperative and postoperative neurological functions were evaluated with AIS grading, ASIA score, residual urine volume and neurophysiological examination. Results showed that in the treatment group 10 patients had a significant clinical improvement in terms of motor, light touch, pin prick sensory and residual urine volume, while nine patients showed changes in AIS grade. Neurophysiological examination was consistent with clinical observations. No sign of tumor was evident until 6 months postoperatively. In the control group, no improvement was observed in any of the neurological functions specified above. BMMSCs transplantation improves neurological function in patients with complete and chronic cervical SCI, providing valuable information on applications of BMMSCs for the treatment of SCI.