Objective To investigate the osteogenic effect of mechanical stretch on cultured flavum ligament cells derived from thoracic ossification ligament flavum patients. Method Flavum ligament cells were isolated and cultured in vitro. Under mechanical stretch, alkaline phosphatase (ALP) activity in cell layers and the mRNA expressions of osteocalcin (OC) were detected by PNPP method and real-time PCR respectively. Results The ALP activity and the mRNA expressions of osteocalcin were both increased under mechanical stretch. Conclusion These results suggest that mechanical stretch plays important roles in the progression of Thoracic ossification of ligamentum flavum(TOLF) through induction of osteogenic differentiation of TOLF cells.