Abstract: Objective To detect the effect of phytoestrogen on DMBA induced breast cancer development of young female SD rats. Methods The 30 rats were randomly divided into two groups:experimental group and control group.All rats were given DMBA,the experimental group was additionally fed with soy isoflavones,and the incidence of breast cancer,the tumor diameter,the results of immunohistochemistry were compared between the two groups. Results For the young SD rats,phytoestrogens can significantly reduce the DMBA-induced breast cancer incidence,tumor size,and immunohistochemical results(P<0.05). Conclusion Phytoestrogens can reduce young female SD rats incidence of breast cancer induced by DMBA.Early childhood interventions can reduce the incidence of breast cancer and improve the prognosis.