Basic fibroblast growth factor (bFGF) has been shown to maintain the osteogenicity of bone marrow derived mesenchymal stem cell (MSCs) in vitro. This study was to investigate whether bFGF with osteogenic supplements could enhance bone formation of posterior spinal fusion. Rabbit bone marrow derived mesenchymal stem cells were selected by adherence on plastic culture-ware. The MSCs were exposed to dexamethasone with (bFGF group, n=6) or without bFGF (OS group, n=6). Treated cells of two groups were seeded on β-tricalcium phosphate ceramics for one day and then implanted onto L5 and L6 transverse processes of the same animal in posterior spinal fusion without decortication. The ceramics acted as control (n=6). Three fluorochromes were injected sequentially as tetracycline at week 2, xylenol orange at week 4 and calcein at week 6. The spinal segments were harvested at week 7. The bone mineral content (BMC) and volume of transverse processes was measured by peripheral quantitative computed tomography. The specimens were underwent undecalcified histology. The mineralization process was examined by fluorescent microscopy. The BMC of transverse processes in OS group was 16% greater than bFGF and control group significantly. The volume of transverse process in OS and bFGF group was significantly greater than control group by 54% and 46% respectively. The volume of transverse processes in OS group was 6% greater than bFGF group though not statistically significant. In histology, newly formed bone grew from two processes towards each other resulting in a relatively short gap distance in OS and bFGF group while less regenerated bone was observed in the control group. At the mineralization front, calcein which was injected into animal at week 6, was predominately labeled in bFGF group. In OS group, both xylenol orange (at week 4) and calcein labeled were found. In conclusion, mesenchymal stem cells pre-exposed to bFGF were not found to give additional enhancement effect on bone formation in the posterior spinal fusion model.