In the general, Disodium estdronate (EHDP) had effects of inhibition in bone resorption, dissolution of hydroxyapatite crystal and decreasing the turn over rate in Paget's disease. Clinically it is used as the drug of treatment for the osteoporosis, heterotropic ossificatiom and Paget's disease inspite of some, controvesies, but there is few article about the effect of EHDP on osteoblast. Authors tries to observe the effect of EHDP on osteoblast using the MC3T3-El osteoblast cell line which has very similar chrateristics with human osteoblast and evaluate the effect by the criteria of changes of morphology, number of osteoblast, and alkaline phosphatase activity. The results are obtained as following: l. EHDP has direct inhibitory effect on the proliferation of osteoblast. 2. EHDP increase the alkaline phosphatase activity in vitro.