Platelet-rich fibrin (PRF) has simple manufacturing process without risk of immunologic rejection or infection by additional materials. This study was designed to investigate the effects of platelet-derived growth factors and transforming growth factors-β in PRF on the proliferation and differentiation of osteoblasts. The authors analyzed platelet-derived growth factors and transforming growth factors-β in normal human serum (NHS) and PRF by enzyme-linked immunosorbent assay quantitatively and those in PRF group were significantly increased when compared with NHS. After harvesting osteoblasts from iliac bone, the authors added 10% fetal bovine serum, 10% NHS, and 3% PRF to osteoblasts, respectively and incubated for 24, 48, 72 hours. For analysis of osteoblast proliferation and differentiation, the authors measured DNA synthesis by [3H]-thymidine isotope activity, protein synthesis by sulforhoamine B assay and those were increased according to elapsed time in all groups, but they were significantly increased in 3% PRF. The authors measured alkaline phosphatase activity of osteoblasts, it was increased according to elapsed to time in all groups, but significantly increased in 72 hours. In conclusion, application of PRF to bone defect sites may have an enhanced effect of bone regeneration with low risk of complications, and relatively simple manufacturing process.