Objective To investigate the effect of intermittent tensile strain on the proliferation and osteogenic differentiation of rBMSCs (rat bone mesenchymal stem cells). Methods Intermittent tensile strain was applied on rBMSCs in vitro by Flexcell 4 000 Tension System (10% elongation amplitude, 0.5 Hz, twice every day, 4 h every time), then effects of the strain after 1, 3, 5, 7 d on cell morphology, cell proliferation, and the relative expression of Cbfα1（core binding factor α1），ALP and collagen I mRNA as well as Cbfα1 protein were measured. Results Intermittent tensile strain slowed the proliferation of rBMSCs from the first day to the seventh day. The relative expression of ALP and collagen I mRNA increased by 3~6 times from the third day（P＜0.05）, meanwhile the expression of Cbfα1 mRNA and protein was up-regulated under the mechanical stimulation. Conclusions Mechanical stretch plays an important role in the proliferation and differentiation of rBMSC, and approprite intermittent tensile strain can slow the proliferation of rBMSC and promot its osteogenic differentiation.