Objective: To investigate the clinical and ultrasonic monitoring value of endometrial and ovarian lesions in patients aged 55 and below after breast cancer surgery Methods: Retrospective analysis of Beijing Obstetrics and Gynecology Hospital and Daxing Teaching Hospital of Capital Medical University with all patients aged 55 and younger after breast cancer surgery from January 2011 to October 2021,a total of 148 cases were suspected to have uterine and ovarian lesions.all cases were made the diagnosis scraping the operations or the endometrial tissue pathology or make follow-up observations. According to the histological and pathological results, X2 test and independent sample T test were used to analyze the characteristics of malignant lesions of uterus and ovary in patients aged 55 and below after breast cancer surgery, and the value of transvaginal ultrasound monitoring endometrial malignant lesions was analyzed by statistical integral quantification method. Results: Firstly, 87 cases were divided into TAM group and 61 cases were divided into non-TAM group according to whether tamoxifen TAM was used. According to the proportion of benign and malignant endometrium in endometrial curettage and surgical pathology, a statistical comparison was made, P=0.712. Then, the general data and ultrasonographic indicators of all the patients in the benign group (128 cases) and the malignant group (20 cases) were statistically analyzed. There were significant differences in body mass index (P=0.048), postoperative time of breast cancer (P=0.000), family history (P=0.005) and clinical symptoms (P=0.000) between the two groups. There were significant differences in endometrial echogenicity (P=0.038), endometrial cystic changes (P=0.038), endometrial fleshy changes (P=0.000) 、whether there is uterine effusion (P=0.000)and endometrial arterial blood flow (P=0.000). In the evaluation of endometrial malignant lesions by means of integral quantification of ultrasonic indicators, the sensitivity and specificity of the diagnosis were 70% and 82% when the ultrasound score was ≥2, while the sensitivity was 40% lower when the ultrasound score was ≥3, but the specificity was 96% higher. In this study, ovarian masses were found in 63 of 148 patients with breast cancer, 62 cases were cystic, some cystic with fine septum, and 1 case was cystic solid. Surgical pathology was benign or narrowed or disappeared during follow-up. Conclusion: In this study, there was no significant difference in the incidence of endometrial malignant changes between patients who took TAM after breast cancer surgery and those who did not. In this study, the overall incidence of endometrial malignancy was relatively high, accounting for 13.5%. Clinically, patients with breast cancer after surgery had increased body mass index, had a longer postoperative period of breast cancer, had a family history of malignant tumor and had gynecological clinical symptoms, had an increased probability of endometrial malignancy. Ultrasound images showed uneven endometrium echo, endometrium polypoid changes，uterine cavity effusion and the presence of endometrium arterial blood flow. However, ovarian lesions in breast cancer patients were benign or self-absorbed. In clinic, we can try to evaluate endometrial malignant lesions by means of integral quantification of ultrasonic indicators