Abstract: Objective: To explore the influence of local injection of astragalus polysaccharides on the expression of bone morphogenetic protein 2 in rats during the retention stage after orthodontic tooth movement. Methods: Forty-eight male Wistar rats (8 weeks old) were divided into 8 groups randomly, each group had 8 rats. Eight groups were the blank group (1 group), the control group (CG, 1 group) and the experimental group (EG, 6 groups). The maxillary right first molar mesialization was performed through a 50 g force for 21 days to establish orthodontic tooth movement model. Ten mg/L astragalus polysaccharides (50μL) were locally injected under the distal buccal periosteum of the maxillary right first molar once every three days. The same volume of saline was injected in the CG. These forces were kept for 1, 3, 7, 14, 21, 28ds and followed by animal sacrifice. The recurrent distances of the first molars were measured. Morphology changes of periodontal tissue were observed by hematoxylin-eosin staining. The expression of BMP-2 in periodontal tissue was determined by immunohistochemistry staining. Results: The width of periodontal ligament in the EG were kept well. The recurrent distances in each group of the EG were shorter than the CG except the 1d group (statistically significant differences, P＜0.05). During the retention stage, the expression of BMP-2 was decreasing in the distal side of the CG, while the EG increased. Compared with the EG of the same time, the expression of BMP-2 in the EG is notably higher (statistically significant differences, P＜0.05). Conclusion: Local injection of astragalus polysaccharides can increase the expression of BMP-2 in the periodontal tissue of rats during the retention stage after orthodontic tooth movement, so as to promote the