Fermented soybean extracts containing large amount of isoflavone aglycones were prepared from Korean traditional fermented soybean paste (KFSP) to examine beneficial effect of isotlavone aglycones-rich KFSP on bone formation activities of osteoblastic cells. To determine positive effects of KFSP on osteoblastic differentiation, alkaline phosphatase activity was measured as phenotypic marker for early stage in osteoblastic differentiation and osteocalcin (OC), and type I collagens were measured as terminal stage markers of differentiation in MG-63 cells. Stimulatory effects of KFSP on bone morphogenic protein-2 (BMP-2), important inducer of differentiated factors for bone formation, remodeling, and mineralization, was examined. Soybean paste fermentation produced higher amount of isoflavone aglycones. KFSP more effectively stimulated production of BMP-2 and increase levels of alkaline phosphatase, OC, type I collagen, and bone mineralization during osteoblastic MG-63 cell differentiation than non-fermented soybean paste extracts.