Abstract: Objective To evaluate the effects of so ybean isoflavone supplementation on alveo lar bone absorption in ost eoporosis rats with experimental periodo ntitis.Methods Fifty female SD rats were randomly divided into 5 groups,including sham group,Ovx group.Twenty-eight days later,the upper first molars were placed ligature to induce periodontitis.On the 65th day,the periodontal bone loss(PBL)and periodontal bone support(PBS)were measured,and the serum bone metabolism index,such as total alkaline phosphatase(AKP),tar trate-resistant acid phosphatase(TRAP)and bonegla protein(BGP) were also deter mined.Results PBL,PBS,AKP,TRAP and BGP in soybean iso flavone groups showed significant difference with the Ovx group(P<0.05),but no difference with sham group and estrogen control group(P>0.05).Conclusion Estrogen deficiency is one of the factors that cause alveolar bone abso rption in rats with experimental periodontitis,and supplementation of soybean isoflavone can effectively prevent the decrease of alveolar bone height and teeth loss.