Background: In previous studies by the authors, it was demonstrated that a fibronectin ( FN)- derived oligopeptide, termed F20, stimulates osteoblast differentiation in vitro and bone formation in vivo. However, the fundamental molecular mechanism by which F20 stimulates osteogenesis remains unknown. Therefore, in this study the molecular mechanism underlying the effect of F20 in osteoblast differentiation is investigated. Methods: The role of F20 in osteoblast differentiation was examined using mouse bone- marrow- derived ST2 cell line. The effect of Smad1/ 5 was determined following small interfering RNA knockdown. Runt- related transcription factor ( Runx) 2, alkaline phosphatase ( Alp), and osteocalcin ( Oc) mRNA levels were determined by quantitative real- time polymerase chain reaction, and their transcriptional activation was assessed using luciferase reporter assays. Extracellular signalregulated kinase ( ERK) phosphorylation was visualized via immunoblotting. Results: Synthetic oligopeptide F20 stimulated expression of bone marker genes Runx2, Alp, and Oc in ST2 cells via Smad and ERK or mitogen- activated protein kinase signaling pathways as did bone morphogenic protein 2 ( BMP2). Furthermore, Runx2 acted as a transcription factor during F20induced osteoblast differentiation. Conclusions: Collectively, these results indicate that F20 induces osteoblast differentiation with a pattern similar to that mediated by BMP2 signaling pathway. The authors' previous data also showed that FN- derived oligopeptide improved wound healing, and it is suggested that F20 might serve as a therapeutic biomolecule to facilitate periodontal tissue regeneration.