Objective To explore the potential of bone marrow mesenchymal stem cells (MSCs) to be modified by neurotrophin3 (NT-3) gene and pretreated with retinoic acid (RA) to differentiate into neuronlike cells in the transplanted site of the spinal cord injury. Methods MSCs, RAinduced MSCs, LacZ gene modified MSCs, NT-3 gene modified MSCs, and MSCs both modified by NT-3 gene and pretreated with RA were immediately transplanted respectively into the completely transected site (TSUB>10/SUB> spinal segment) of spinal cord. On the 67th day after the operation, the spinal cord segment was removed and frozenly sectioned. The differentiation potential of MSCs was examined by immunofluorescence histochemistry and the percentage was calculated of neuronlike cells that were differentiated from MSCs among all the transplanted cells groups. Results Transplanted MSCs could differentiate into neural stem cells (nestinpositive), neuroglial cells (GFAPpositive) and neuronlike cells (NF and MAP2positive) in the injured spinal cord. Some of them also differentiated into the neuronlike cells which contained some neurotransmitters (ChAT and 5-HT positive) or had the potential to form a synapse (PSD95_positive). The percentage of neuronlike cells differentiated from MSCs modified by NT-3 gene and pretreated with RA was the highest among all the transp