The bone formation and re-formation are regulated by two factors that are the synthesis of bone matrix by osteoblast and reabsorption by osteoclast. Recently, there are many studies about regeneration and healing of bone tissue by activation of osteoblast. In general, it is known that the activation of osteoblast is influenced by not only biological stimulus but physical stimulus. In this study, we verified that ostoeblast activation was influenced by low intensity ultrasound. Various ultrasonic properties were used to find out the most appropriate condition on cell activation. From this study, we could confirm that 0.3W/$ extrm{cm}^2$ intensity of ultrasound was the most appropriate to tell activation over whole duty cycles and the increasing rate of tell was the highest at 50％ duty cycle. Thus, it is expected that optimal ultrasonic characteristics on regeneration of bone matrix may be applied to fracture and osteoporosis healing.