Objective: to investigate the effective method of transvaginal ultrasound monitoring endometrial lesions in breast cancer patients treated with tamoxifen TAM.Materials and methods: retrospective analysis in January 2010 - January 2019 maternity hospital affiliated to the capital university of medical sciences, Beijing, and Beijing daxing district people"s hospital, a total of 94 cases of postoperative breast cancer patients taking TAM, for suspected endometrial lesions for medical or surgical histopathological results were, pathology and transvaginal ultrasound results contrast analysis.Results: 94 cases of breast cancer patients, 78 cases of endometrial pathologic benign group (including normal endometrium, 8 cases, hyperplasia and complex hyperplasia of 32 cases, 28 cases polyps and polypoid hyperplasia and 10 cases of atrophic endometrium), 16 cases of malignant group (including 5 cases with atypical hyperplasia, well-differentiated adenocarcinoma in 2 cases, 5 cases were low differentiated adenocarcinoma, serous carcinoma 2 cases, malignant mesoderm mixed tumor 1 case, clear cell carcinoma 1 case).The comparison of transvaginal ultrasound data between the two groups showed that there were significant differences in endometrial echogenicity, whether the endometrial had small cystic changes, whether the endometrial had polypoid changes, the boundary between the endometrial and muscular layer, and the presence of intrauterine effusion.There was no significant difference in endometrial thickness.Conclusion: postoperative breast cancer patients taking TAM transvaginal ultrasound examination such as endometrial echo inequality, endometrial appears polypoid change, lining and muscle layer boundary is not clear and uterine cavity accumulates fluid to possible endometrial enough, should prompt clinical histopathological examination and curettage line as soon as possible, while endometrial occurrence utricle is benign endometrium high risk.