BACKGROUND: Spinal cord injury (SCI) is one of the most severe central nervous system injuries. Currently, transplanting bone marrow mesenchymal stem cells (BMSCs) is considered a therapeutic option for SCI. Tanshinone IIA (TIIA) is one of the extracts obtained from Salvia miltiorrhiza Bunge, which has been shown to have some protective effects against SCI. The present research was aimed to explore whether TIIA would influence the fate of transplanted BMSCs in a rat model of SCI, especially with regard to their differentiation into neuronal cells. METHODS: Bone marrow mesenchymal stem cells were obtained from immature rats and identified using flow cytometry. After SCI, 1.0?×?10(7) cells labeled with PKH67 were transfused into the injured spinal cord. TIIA was first injected into the tail vein (30?mg/kg) 1?h before surgery. From day 1 to day 7 post-SCI, TIIA was injected (20?mg/kg) per day at the same time. Recovery of locomotor function and histological regeneration of the spinal cord were compared among the groups, with the differentiation and distribution of BMSCs determined anatomically and biochemically by the expression of neural cell markers. RESULTS: Locomotor assessments showed that the rats in the BMSCs?+?TIIA group exhibited higher scores (19.33?±?0.58) than those in the other groups (13.67?±?1.53, 17.67?±?0.58, 18.00?±?1.73). The area of the cavity in the BMSCs?+?TIIA rats was smaller than that in the other groups (1.30?±?0.56, 10.39?±?1.59, 6.84?±?1.18, 4.36?±?0.69). Co-expression of glial fibrillary acid protein was observed in transplanted BMSCs, with a reduced rate in the BMSCs?+?TIIA group relative to that in the SCI group. In contrast, the expression levels of Nestin, neuron-specific nuclear protein (NeuN) and neurofilament protein 200 (NF200) were greatest in the transplanted cells in the BMSCs?+?TIIA group. CONCLUSIONS: Tanshinone IIA treatment enhances the therapeutic effects of BMSC transplant on SCI, likely by?promoting the differentiation of?neuronal cells.