The inhibition of osteoblast by glucocorticoid is recognized as its action mechanism of decreased bone formation. In this study, the effect of JY, Jahyulyangkeuntang, on the differentiation and mineralization of osteoblastic cells was investigated in the presence of dexamethasone. The cell counting, enzyme activity assay, MTT assay, collagen content assay were done to determine the cell proliferation, alkaline phosphatase(ALP) activity, bone martrix production, and cell apoptosis. JY enhanced the cell proliferation after the culture for 10 days. ALP activity and total protein synthesis, and intracellular collagen synthesis were increased when the cells were treated with JY. And JY restored calvarial cell function decreased by dexamethasone.