A four-point bending device was used to investigate the effect of stretching on osteoblasts collagen production. Cells were stretched with different strain level and loading time. Cyclic stretching of the cells with a strain magnitude of 500 με resulted in an increased collagen production while collagen synthesis was significantly reduced with a strain magnitude of 1 000 με and 1 500 με (P＜0.01). A new loading method, step increased stretching was also used. Cells were stretched at 500 με firstly, followed by stretching at 1 000 με for the same hours. Then the strain level was raised to 1 500 με and cells were stretched for the same hours. The step increased stretching experiment showed that osteoblasts absorbed proline to synthesize collagen when received an appropriate signal (500 με). When the strain magnitude was raised, that is to say, the mechanical stimulation was turned into an inhibiting signal, intracellular ³H-proline was released into solution again. These results demonstrate that osteoblasts can adjust themselves to adapt the new mechanical stimulation during the step increased stretching course.