Objective To investigate the effect of frequency on osteoblast apoptosis induced by tensile strain. Methods MC3T3-E1 cells were applied with 1% biaxial tensile strain at the frequency of 1, 2, 3, 4, 5 Hz, respectively for 1 hour per day in 8 days. The survival rate of the cells was determined by activity of lactate dehydrogenase (LDH). Annexin V-FITC/ PI Flow cytometry was used to test cell apoptosis. Real-time RT-PCR was used to detect the gene level of apoptosis markers caspase-3, -9 as well as Bcl-2 and Bax, and Western blotting was used to test protein expressions of caspase-3, -9. Results Different loading frequencies had no effect on osteoblast activity of LDH. There was no significant difference in the total apoptosis rate of flow cytometry at different frequencies. However, the frequency of 2 Hz could induce early osteoblast apoptosis. Tensile strain at the frequency of 2 Hz could significantly increase the expression of caspase-3, -9 gene and protein, and induce cell apoptosis with the up-regulation of the Bax/Bcl-2. Conclusions Osteoblast apoptosis and death cannot be induced by 1% biaxial tensile strain at the frequency of 1-5 Hz, but the frequency of 2 Hz can induce the early apoptosis of osteoblasts by up-regulating the expression of Bax/BCl-2.