Bisphosphonates have been widely used to treat metabolic bone diseases, although the . mechanism of bisphosphonate action on bone has not been fully understood. This study aimed to examine the direct action of pamidronate on cell proliferation and differentiation of cultured human mesenchymal stem cells(hMSC). Four experimental groups and two control groups were designed; Experimental groups included both osteogenic supplement(OS) and pamidronate-treated group, pamidronate-treated group after 1 week OS treatment, only pamidronate-treated group, OS-treated group after 1week pamidronate treatrnent. Control gr。니ps included DMEMtreated group and OS-treated group. Human MSCs were isolate from bone maπow ， and cultured for 7, 14, 21 days. For the detection of osteoblastic differentiation, AI.Pase activity was measured and the expression of type 1 collagen and osteocalcin were evaluated. Von Kossa’s silver stain was performed for the examination of calcification. As results, the proliferation rate of 바1SC was maintained to be more than 90% by 1uglml of pamidronate. AI.Pase activity showed the highest value at the concentration of 100nglml of pamidronate. In pamidronate-treated group, ALPase activity reached a peak at the third week and the expression of type 1 collagen mRNA and protein was enhanced compared to other experimental and control groups, whereas osteocalcin expression was found only in OStreated group. Calcification was decreased by a dose dependent manner followed by pamidronate treatment. This study su잃，est that pamidronate treatrnent may be able to enhance the osteoblastic differentiation of hMSC at the early stage. On the other hand, calcification appeared to be inhibited by pamidronate treatrnent.