Purpose: Concentrated growth factor (CGF) is an autologous leukocyte- and platelet-rich fibrin biomaterial that has recently been used for bone healing therapy. Previous studies used fibrin membrane or CGF extract without fibrin without soluble factors in vitro. This study investigated the effects of CGF that contained soluble factors on cultured rat bone marrow (RBM) cells in vitro. Furthermore, the effects of CGF implanted in rat calvarial bone defects in vivo were also investigated. Materials and Methods: CGF and platelet-poor plasma (PPP) gel, which both have fibrin networks, were prepared from rat blood. For the in vitro study, CGF and PPP gel were frozen, and thin sections approximately 30 μm thick were cut and coated onto the surfaces of cell disks. RBM cells were then harvested and cultured on the coated disks in serum-free medium. For the in vivo study, rat calvarial bone defects (3.8 mm in diameter) were created and implanted with CGF, PPP gel, or left unfilled. Results: In vitro, the actin stress fibers of RBM cells cultured on disks coated with CGF or PPP gel tended to extend more than cells cultured on uncoated disks. However, no significant difference was observed in terms of cell morphology between RBM cells cultured on CGF- and PPP gel-coated disks. Cell proliferation and osteoblastic differentiation were significantly higher in cells cultured on the CGF-coated disks than on the PPP gel-coated disks. In vivo, more new bone had formed in defects treated with CGF than in defects treated with PPP gel. Conclusion: In this preliminary study, fibrin and soluble factors in CGF promoted initial cell stretching, proliferation, and osteoblastic differentiation of RBM cells in vitro and bone regeneration in rat calvarial bone defects in vivo. Keywords: bone healing, bone marrow, calvarial bone defect, concentrated growth factor, platelet-poor plasma gel