Maxillary sinus lifting procedure and bone grafting are used to reconstruct atrophic maxillae. These procedure are usually followed by the placement of endosseous dental implants. Different materials and techniques can be used for sinus bone grafting. Platelets are known to contain various growth factors involved in the repair of the vasculature and tissues, and it is known that the specialized platelet secretory granules, the alpha granules, contain platelet derived growth factor(PDGF), transforming growth factor-beta(TGF-beta), insuline like growth factor-I(IGF-I), epidermoid growth factor(EGF), and others. This study was to evaluate the effect of PRP on bone formation in a sinus bone grafting. Twelve rabbits were included in this randomized, blinded, prospective pilot study. In experimental group, sinus bone grafting with autobone and platelet rich plasma. In control group, sinus bone grafting with only autobone. Rabbits were sacrificed at 2nd, 4th, 8th, 12th weeks postoperatively. Clinical and radiographic tests, histological analysis were conducted to compare both sides. In clinical examination, there in no significant difference between experimental group and control group. But, in radiographic examination, a distinct incresed in the radiopaque of the PRP experimental group at 2nd and 4th weeks. The histologic examination revealed that more new bone formation and osteoblast activity were seen in experimental group at 2nd and 4th weeks. In conclusion, PRPs action in sinus bone grafting had a capacity of increased new bone formation in a early bone healing stage.