Polygoni Multiflori Radix (PMR) a dried root tuber of Polygonum multiflorum Thunberg with bioactivities in bone metabolism is one of the most famous tonic traditional medicines in China, Japan and Korea.To observe the anti-osteoporotic effect of PMR, we observed the effects on proliferation and alkaline phosphatase (ALP) activity of primary osteoblasts, bone nodule formation, pit formation of osteoclasts and osteoclastogenesis in vitro. As the result of that, although PMR extracts have no meaningful changes on the the proliferation of primary osteoblasts, significant (p < 0.01) increases of ALP acitivity of osteoblasts were dose-dependently observed in all PMR extracts treated groups tested compared to that of vehicle control. It means that it enhanced the differentiation (ALP activity) and bone nodule formation of osteoblast. In addition, PMR extracts dose-dependently inhibits the pit formation and the number of multinucleated osteoclast-like cells (OCLs), osteoclastogenesis in vitro. Therefore these results show the possibility of PMR extracts as another anti-osteoporotic agents.