ObjectiveTo explore the function of flaxseed powder lingans on the prevention of breast cancer and the relation with estrogen on the ovariectomized female rats. MethodsFouty-eight female wistar rat were randomly divided into basal diet group(BD), basal diet castrate group (BDC), flaxseed group(FS) and flaxseed castrate group(FSC), All of the rats were treated with DMBA by intragastric administration at a dose of 2mg/kg weight to establish the experimental animal models of induced breast cancer and the BDC and FSC groups were operated for the ovariectomy. On the 21 week the volume and weight of the palpable tumors were measured and conducted pathological examination by pathologist. ResultsThe experimental animals were generally in well situation, there was no obvious toxic or side effect in experimental groups, palpable tumors appeared two to four weeks later in FS and FSC groups than that in the control; Compared with the control groups, the incidence and the average number of lesions of breast hyperplasia, atypical hyperplasia, breast cancer were significantly lower in flaxseed groups(hyperplasis:FS vs BD,P=0.006**；FSC vs BDC,P<0.001**; atypical hyperplasia:FS vs BD,p=0.048*；FSC vs BDC,P <0.014*; breast cancer:FS vs BD,P=0.028*；FSC vs BDC,P=0.047*), additionally, the volume and weight of the tumors were lower in flaxseed groups. The results also suggested that the ability of inhibiting the hyperplasia and tumor cell growth of the flaxseed lignans is related with estrogen states(hyperplasis:P=0.008**；atypical hyperplasia: P=0.042*；Breast cancer:P=0.033*). ConclusionsFlaxseed powder lignans can effectively prevent and reduce the occurrence of breast cancer, precancerous lesions and hyperplasia induced by DMBA, and the preventive effect of flaxseed powder lignans are affected by body estrogen. The above results may be of reference value for screening effective population and preventing breast cancer by lignans.