Objective To study the short time effects of cyclic mechanical stretch on human adenocarcinoma cell line A549. Methods By Flexercell-4000TTM Unit, A549 cells were subjected to 20% elongation of biaxial stretch at frequency 30cycles/min within 4h. Results Short time mechanical stimulation can enhance the proliferation rate of A549 cells. The proliferation responding ratio M(%) vary with the loading time: M(%)=18% for 0.5 h, M(%)=22% for 1 h and M(%)=5% for 4 h. Conclusion There seems to be a peak of M(%) when the cycle number is about 1800 cycles. This feature is similar to the human bone derived cells. Further experiment demonstrates that intermittent loading could result in high proliferation of the A549 cells for long time whereas the past studies showed the continuous loading can only depress A549 cells proliferation.