To study the effects and importance of fluoride on FBs in the development of extraperiosteal calcification and the ossification of skeletal fluorosis, the presence of the osteogenic phenotype, which is indicated by the expression of core-binding factor a1 (Cbfa1) and osteocalcin (OCN), in an FB cell line (L929) and in osteoblasts (OBs) exposed to fluoride was determined. Fibroblasts and osteoblasts were exposed to different concentrations of fluoride (0, 0.0001, 0.001, 0.1, 1.0, 10.0 and 20.0mg/L F-). By using RT-PCR and ELISA, the mRNA levels of Cbfa1 and OCN were measured at 48h, and the protein levels of Cbfa1 and OCN were measured at 2, 4, 24, 48 and 72h. The data demonstrated the following: (1) The Cbfa1 protein level in fluoride-treated fibroblasts clearly increased at 48h in the groups treated with 0.0001, 0.001, 0.1, 1.0 and 20.0mg/L F-. The Cbfa1 protein level of the group treated with 10mg/L F- at 72h was higher than that of the control group. The level of Cbfa1 mRNA in the fibroblasts was much higher at 48h in the group treated with 10.0mg/L F- than in the control group. (2) The OCN protein level in fluoride-treated fibroblasts was significantly higher than that of the control group in the 0.0001, 0.1, 1.0, 10.0 and 20.0mg/L F- groups at 2h, and in the 0.001 and 0.1 F- groups at 4h. A slightly higher level of OCN mRNA in fluoride-treated fibroblasts was also found in the 1.0 and 20.0mg/L F- groups compared to the control group. (3) The expressions of Cbfa1 and OCN in osteoblasts treated with the same experimental conditions as the fibroblasts were up-regulated by fluoride following the same trend as in the fibroblasts. Our results showed an increase in the expression of Cbfa1 and OCN in fibroblasts and osteoblasts exposed to fluoride and suggested that the osteogenic function of fibroblasts induced by fluoride could play an important role in the development of extraperiosteal ossification during skeletal fluorosis.