BACKGROUND: In recent years, the development of tissue engineering has provided a new approach for the treatment of periodontal bone defect. Tissue engineering therapy includes seed cells, scaffolds and growth factors. Platelet gel contains a large number of platelet growth factors, and collagen is often used for the preparation of scaffold materials. Therefore, the platelet gel and collagen biologically active composite membrane can provide scaffolds and growth factors for the defect bone. OBJECTIVE: To investigate the effect of autologous platelet gel-collagen biologically active composite membrane on the repair of periodontal bone defect in rats. METHODS: Forty-two Wistar rats (Shanghai Xipuer-Bikai Experimental Animal Co., Ltd., China) were selected. (1) Collagen was cut into 5 mm×2 mm size, and 10 mL of whole blood was extracted from 6 rats to obtain platelet-rich plasma. Autologous platelet gel-collagen composite membrane was prepared by adding bovine thrombin, calcium chloride and collagen in a certain proportion. Platelets in whole blood and in platelet-rich plasma were detected. The levels of platelet derived growth factor AB, transforming growth factor-β, basic fibroblast growth factor and vascular endothelial growth factor in whole blood and platelet-rich plasma were detected by ELISA. (2) The models of mandibular periosteal defect were established in 36 rats (the size of the bone defect was 5 mm×2 mm, and the root surface cementum was removed) , and randomly divided into two groups. Autologous platelet gel-collagen group placed the autologous platelet gel-collagen composite membrane in the bone defect, and the control group did not place any materials. The hematoxylin-eosin staining of periodontal tissues of rats in each group was analyzed at 2, 4 and 8 weeks after surgery. Rate of new born, new centumum formation, new alveolar bone formation, and new periodontal ligament tissue formation height were measured. The expression of bone morphogenetic protein-2 was detected by immunohistochemical staining. RESULTS AND CONCLUSION: (1) The mean platelet count in platelet-rich plasma was 4.78 times as high as the whole blood, indicating that the number of platelets increased significantly after prepared into platelet-rich plasma (P < 0.05) . The levels of platelet derived growth factor AB, transforming growth factor-β, basic fibroblast growth factor and vascular endothelial growth factor in platelet-rich plasma were 3.10, 3.45, 7.17 and 5.45 times of the whole blood, respectively (P < 0.05) . (2) The results of hematoxylin-eosin staining observed that the rate of new born, new centumum formation, new alveolar bone formation, and new periodontal ligament tissue formation height at 2 weeks in the autologous platelet gel-collagen group showed no significant difference from the control group (P> 0.05) . At 4 and 8 weeks, all above indexes in the autologous platelet gel-collagen group were significantly higher than those in the control group (P < 0.05) . (3) Results of immunohistochemical staining revealed that at 2 weeks, bone morphogenetic protein-2 in the autologous platelet gel-collagen group began to express, and the expression of bone morphogenetic protein-2 was highest at 4 weeks (P < 0.05) , and the positive expression was weakened at 8 weeks (P> 0.05) . (4) Our results clarify that autologous platelet gel-collagen bioactive composite membrane can significantly promote the regeneration of new tooth, which is associated with the expression of bone morphogenetic protein-2, and reduce the repair time after periodontal tissue defect.