Objective: Cells are exposed to mechanical forces of different types every day and respond to these mechanical loads with changes in their structure and function. Functional changes include growth, gene expression pattern, protein synthesis, differentiation and cell movement. Mesenchymal stem cells (MSCs) are undifferentiated and prone to convert to osteoblast, myoblast, chondrocyte and adipocyte. So these cells have been selected for tissue engineering and regenerative medicine. Mechanical stimulation has been shown to promote osteogenic differentiation of MSCs. Materials and Methods: Bone marrow-derived stem cells were isolated from a rat and cultured in α-MEM medium containing 10% FBS. Multipotential property of cells was examined by incubating cells in chondrogenic and adipogenic mediums and flow cytometry method was performed to verify the purity of isolated cells. Four test groups were assigned in this research:mechanical, chemical, mechanical/chemical and control groups. In mechanical group MSCs were seeded on collagen I coated membrane and exposed to cyclic uniaxial stretch of 3% and 0.3 Hz frequency for 24 hours by a cyclic stretch device fabricated in National Cell Bank of Iran. In chemical group cells were treated with culture medium supplemented with 1 μM dexamethasone, 10 mM β-glycerophosphate and 0.1 mM ascorbic acid for 10 days. In mechanical/chemical group, cells were subjected to the strain for 24 hours and then cells were incubated in osteogenic medium for 10 days. Real-Time PCR carried out to evaluate the expression of osteogenic marker genes (Runx2 and OCN). Results: Real-time results showed the expression levels of Runx2 and OCN were much more increased in mechanical/ chemical group in comparison to mechanical and also chemical ones. Conclusion: Combination of mechanical strain and chemical factors is much more suitable for directing osteogenesis and these two elements enhance each other.